research on acid rain

October 25, 2023

The World Solved Acid Rain. We Can Also Solve Climate Change

Lessons from how we tackled acid rain can be applied to our world today

By Hannah Ritchie

Thomas Fuchs

The world feels like it’s being set alight; wildfires in Canada and Europe, floods in China, and a never-ending stream of recording-breaking heat waves have garnered numerous headlines.

The feeling that time is quickly running out is very real . And it’s easy to believe that the world cannot tackle big environmental problems. This sense of helplessness is something that I have personally battled for more than a decade. But that feeling is a barrier to action: Nothing has changed when we’ve called for action before, so why should we expect any different this time?

But our past efforts tell us there is hope. The world has solved large environmental problems that seemed unsurmountable at the time. In my role at Our World in Data, I’ve spent years looking at how these problems have evolved, and I think that it’s worth studying these issues, not only for hope, but to understand what went right and what can help us face today’s crises. An eye-opening example is acid rain; studying how the world tackled this geopolitically divisive problem can give us some insights into how we can tackle climate change today.

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It has mostly slipped from the public conversation, but acid rain was the leading environmental problem of the 1990s. At one point, it was one of the biggest bilateral diplomatic issues between the United States and Canada.

Acid rain—precipitation with high levels of sulfuric or nitric acids—is mostly caused by sulfur dioxide, a gas that is produced when we burn coal. It had severe effects on ecosystems. It dissolved old sculptures , stripped forests of their leaves, leached soils of their nutrients, and polluted rivers and lakes . Emissions from the U.K. would blow over to Sweden and Norway; emissions from the U.S. would blow over to Canada. Just like climate change, it crossed borders, and no country could solve it on its own.

This is a classic game theory problem; outcomes don’t only depend on the actions of one country but on the actions of the others too. Countries will only act if they know that others are willing to do the same. This time, they did act collectively. Government officials signed international agreements , placed emissions limits on power plants and started to reduce coal burning. Interventions were incredibly effective. In Europe, sulfur dioxide emissions fell by 84 percent and in the U.S. by 90 percent . Some countries have reduced them by more than 98 percent.

We did something similar with the ozone layer. The ozone hole was a big coordination problem. No single country was responsible for the world’s emissions of ozone-depleting substances. So there was little upside and some downside to countries taking the lead on their own. They would spend money and implement unpopular environmental policies without making much of a dent in the global problem. The only way to cut emissions substantially was for many countries to join in. It relied on international collaboration. Yet the world solved it. After countries signed the Montreal Protocol, emissions of ozone-depleting substances fell by more than 99 percent .

Credit: John Knight; Source: Data Explorer: Air Pollution, Our World in Data

What we learned from tackling acid rain and the ozone hole can be applied to tackling climate change overall.

First, the cost of technology really matters. The cost-benefit ratio of desulfurization technologies was key to solving acid rain. The cost of installing scrubbers was significant but not budget-breaking. If they had come at a huge cost, countries wouldn’t have made the switch.

Similarly, cheap low-carbon technologies are essential for climate change. Low-carbon technologies used to be expensive, but in the last decade the price of solar energy has fallen by more than 90 percent . The price of wind energy by more than 70 percent. Battery costs have tumbled by 98 percent since 1990, bringing the cost of electric cars down with them. Globally, one in every seven new cars sold is electric . In Europe, one in every five, and in China one in every three.

At the same time, countries are waking up to the potential costs of not moving to clean energy, whether in the form of climate damages—at home or overseas—or being tied to volatile fossil fuel markets.

Second, climate agreements and targets take time to evolve. Negotiations are long. The ozone hole and acid rain were not fixed with the first international agreements on the table. The initial targets were too modest to make a large enough difference . But over time, countries increased their ambitions, amended their agreements and reached for those higher goals.

This is a basic principle of the Paris climate agreement. Countries agreed to step up their commitments to keep global temperature rise below 1.5 degrees Celsius or 2 degrees C . While this has been happening, it definitely hasn’t happened fast enough. The world is on track for an increase of around 2.6 degrees C by 2100. That’s extremely bad. But it’s still a degree lower than where we were heading in 2016. Governments have increased action and increased their target numbers too. And just like with acid rain or the ozone hole, they need to keep aiming higher. If every country fulfilled its pledges, the world would keep temperature rise to 2 degrees C. If they met their net-zero commitments on time, we could sneak below it.

Finally, the stance of elected officials matters more than their party affiliation. Environmental issues do not have to be so politically divisive. Acid rain was a bipartisan divide in the U.S. under Ronald Reagan’s presidency. But it wasn’t a Democrat who finally took action; it was his Republican successor, George H.W. Bush. Before taking office, Bush pledged to be the “environmental president,” a bold stance for many right-wing leaders today, but one that we need to see repeated if we are going to make and reach these loftier goals. In the U.K., there is strong public support for net-zero emissions even among the political right. Margaret Thatcher—arguably one of the U.K.’s most right-wing leaders ever—was one of the earliest to take climate change seriously .

Former German chancellor Angela Merkel is a modern example of a pro-climate conservative leader. A scientist by training , Merkel always acknowledged the threats of climate change, gaining the title of “climate chancellor.” In the late 1990s she led the first U.N. climate conferences and the Kyoto Protocol. In 2007, she convinced G8 leaders to set binding emission reduction targets. It's wrong to frame environmental problems as right-left wing issues. If we’re going to tackle climate change, we need to overcome this divide.

Climate change is not the perfect parallel for the environmental problems we’ve solved before. It will be harder; we should be honest about that. It means rebuilding the energy, transport and food systems that underpin the modern world. It will involve every country, and almost every sector. But change is happening, even if it doesn’t hit the headlines. To accelerate action, we need to have the expectation that things can move faster. That’s where past lessons come in; we should use them to understand that these expectations are not unrealistic. Change can happen quickly, but not on its own; we need to be the ones to drive it.

This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of  Scientific American.

A version of this article with the title “What We Learned from Acid Rain" was adapted for inclusion in the January 2024 issue of Scientific American.

Acid rain, explained

The fossil fuels that humans burn for energy can come back to haunt us as acid rain.

Acid rain describes any form of precipitation that contains high levels of nitric and sulfuric acids. It can also occur in the form of snow, fog, and tiny bits of dry material that settle to Earth. Normal rain is slightly acidic, with a pH of 5.6, while acid rain generally has a pH between 4.2 and 4.4 .

Causes of acid rain

Rotting vegetation and erupting volcanoes release some chemicals that can cause acid rain, but most acid rain is a product of human activities. The biggest sources are coal-burning power plants , factories, and automobiles.

When humans burn fossil fuels , sulfur dioxide (SO 2 ) and nitrogen oxides (NO x ) are released into the atmosphere. Those air pollutants react with water, oxygen, and other substances to form airborne sulfuric and nitric acid. Winds may spread these acidic compounds through the atmosphere and over hundreds of miles . When acid rain reaches Earth, it flows across the surface in runoff water, enters water systems, and sinks into the soil.

A virtual tree graveyard of Norway spruce in Poland bears the scars of acid rain. Caused when rain droplets absorb air pollution like sulfur and nitrogen oxides, acid rain weakens trees by dissolving nutrients in the soil before plants can use them.

Effects of acid rain

Sulfur dioxide and nitrogen oxides are not primary greenhouse gases that contribute to global warming , one of the main effects of climate change ; in fact, sulfur dioxide has a cooling effect on the atmosphere. But nitrogen oxides contribute to the formation of ground-level ozone , a major pollutant that can be harmful to people. Both gases cause environmental and health concerns because they can spread easily via air pollution and acid rain.

Acid rain has many ecological effects, especially on lakes, streams, wetlands, and other aquatic environments. Acid rain makes such waters more acidic, which results in more aluminum absorption from soil, which is carried into lakes and streams. That combination makes waters toxic to aquatic animals. ( Learn more about the effects of water pollution .)

Some species can tolerate acidic waters better than others. However, in an interconnected ecosystem, what affects some species eventually affects many more throughout the food chain, including non-aquatic species such as birds .

Acid rain and fog also damage forests, especially those at higher elevations. The acid deposits rob the soil of essential nutrients such as calcium and cause aluminum to be released in the soil, which makes it hard for trees to take up water . Acids also harm tree leaves and needles.

The effects of acid rain, combined with other environmental stressors, leave trees and plants less healthy and more vulnerable to cold temperatures, insects, and disease. The pollutants may also inhibit trees' ability to reproduce. Some soils are better able to neutralize acids than others. But in areas where the soil's "buffering capacity" is low, such as parts of the U.S. Northeast,   the harmful effects of acid rain are much greater.

Acid deposits damage physical structures such as limestone buildings and cars. And when it takes the form of inhalable fog, acid precipitation can cause health problems in people, including eye irritation and asthma.

What can be done?

The only way to fight acid rain is by curbing the release of the pollutants that cause it. This means burning fewer fossil fuels and setting air-quality standards.

In the U.S., the Clean Air Act of 1990 targeted acid rain, putting in place pollution limits that helped cut sulfur dioxide emissions 88 percent between 1990 and 2017. Air-quality standards have also driven U.S. emissions of nitrogen dioxide down 50 percent in the same time period. These trends have helped red spruce forests in New England and some fish populations , for example, recover from acid rain damage. But recovery takes time, and soils in the northeastern U.S. and eastern Canada have only recently shown signs of stabilizing nutrients .

Acid rain problems will persist as long as fossil fuel use does, and countries such as China that have relied heavily on coal for electricity and steel production are grappling with those effects. One study found that acid rain in China may have even contributed to a deadly 2009 landslide . China is implementing controls for sulfur dioxide emissions, which have fallen 75 percent since 2007 —but India's have increased by half.

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Global Trends of Acidity in Rainfall and Its Impact on Plants and Soil

Jigyasa prakash.

Laboratory of Air Pollution and Global Climate Change, Department of Botany, Institute of Science, Banaras Hindu University, Varanasi, 221005 India

Shashi Bhushan Agrawal

Madhoolika agrawal.

Due to its deleterious and large-scale effects on the ecosystem and long-range transboundary nature, acid rain has attracted the attention of scientists and policymakers. Acid rain (AR) is a prominent environmental issue that has emerged in the last hundred years. AR refers to any form of precipitation leading to a reduction in pH to less than 5.6. The prime reasons for AR formation encompass the occurrence of sulfur dioxide (SO 2 ), nitrogen oxides (NO x ), ozone (O 3 ), and organic acids in air produced by natural as well as anthropogenic activities. India, the top SO 2 emitter, also shows a continuous increase in NO 2 level responsible for AR formation. The plants being immobile unavoidably get exposed to AR which impacts the natural surrounding negatively. Plants get affected directly by AR due to reductions in growth, productivity, and yield by damaging photosynthetic mechanisms and reproductive organs or indirectly by affecting underground components such as soil and root system. Genes that play important role in plant defense under abiotic stress gets also modulated in response to acid rain. AR induces soil acidification, and disturbs the balance of carbon and nitrogen metabolism, litter properties, and microbial and enzymatic activities. This article overviews the factors contributing to AR, and outlines the past and present trends of rainwater pH across the world, and its effects on plants and soil systems.

Introduction

A worldwide increase in globalization and urbanization had augmented the consumption of energy from various sources. The use of fossil fuels mainly coal for the generation of electricity, oil in transport services, and the impact of industrialization has caused a higher degree of concentration of pollutants and particulate matter in the atmosphere, thus enhancing air pollution (Singh and Agrawal 2005 ). Greater access to energy improves both the economic growth and human development of a country, but this increase in energy demand also causes several environmental problems (Liu et al. 2019 ). Although the growth in renewables has been seen in all forms of energy since 2010, the proportion of fossil fuels in global primary energy demand remains above 80% (World Energy Outlook 2019 ). Table ​ Table1 1 shows the scenario of world primary energy demand (past, present, and estimated) by regions from 2000 to 2040. In India, energy demand outpaced global energy growth and oil demand grew by 5% in 2018 (Global Energy and CO 2 Status Report 2019 ). Fossil fuel consumption in India has increased from 208 million tons per year in 2000 to 708 million tons in 2017 (World Energy Outlook 2019 ).

Regional scenario of total primary energy demand by in the world

Values are in MTOE (million or mega tones in oil equivalent), modified from World Energy Outlook 2019

Acid rain (AR) can be defined as a combination of dry and wet deposition from the atmosphere having higher than normal concentrations of nitric (HNO 3 ), sulfuric acids (H 2 SO 4 ), and acidifying compounds which lead to a decrease in the pH of rainwater to less than 5.61. In 1845, AR was first been mentioned by Ducros, although a detailed study of AR was conducted by Robert Angus Smith ( 1872 ) and potentially harmful effects were described. There are various sources and precursors of AR formation that result both from natural and man-made activities. Natural sources are volcanic eruption, decay of vegetation, lightening, and other biogenic activities, while human-induced sources include the burning of coal, natural gas, oil in thermal power plants, and agricultural emissions resulting from the use of fertilizers, pesticides, intensive farming of paddy, and stubble burning (Zhang et al. 2007 ).

AR had arisen as one of the major environmental disasters in countries such as North America, Europe, and East Asia (Singh and Agrawal 2007 ). China suffered from a high frequency of events of acid deposition (Zhou et al. 2019 ). India is the second known emitter of SO 2 , and emissions of both SO 2 and NO x , the major sources of AR, are expected to grow at least until 2030 (Li et al. 2017 ; Andrade et al. 2020 ). The events for the occurrence of acid rain (pH < 5.6) across India showed an increasing trend over the past four decades (Bhaskar and Rao 2017 ). Moreover, emissions from agricultural activities due to excessive use of fertilizers and pesticides add ammonia (NH 3 ) and reactive nitrogen (N r ) species to the atmosphere, which further enhances the acidity of depositions (Sutton et al. 2017 ).

Worldwide occurrence of AR could negatively affect ecosystem components causing forest declines (Zheng et al. 2019 ) and loss of biodiversity, altering litter properties and enhancing soil acidification (Fei et al. 2020 ), leading to declining in soil microbial communities (Wei et al. 2020 ). One of the essential components of terrestrial ecosystems, plant productivity, is also negatively affected by AR pollution (Liu et al. 2018a , b ), leading to loss of leaves, inhibition of growth, premature defoliation or premature aging, necrotic spots, and other visible symptoms (Bobbink et al. 2010 ; Du et al. 2017 ). The aboveground parts get directly affected by AR, thus inhibiting the functions of wax biosynthesis, accumulation of intracellular H + ions, and other harmful ions in mesophyll cells (Shu et al. 2019 ). The excessive accumulation of intracellular H + ions can induce oxidative stress due to the generation of reactive oxygen species (ROS) (Neves et al. 2009 ). Acidification of water bodies makes the environment uninhabitable for plants and local animals and thus causes risks to their survival (Singh and Agrawal 2007 ).

Due to lots of repercussions on the ecosystem, controlling the emissions of acidic depositary compounds in the atmosphere can be one of the best solutions that can be prioritized. Several steps were employed globally to decrease the emissions of SO 2 and NO x like the use of cleaning technologies and equipment such as efficient boilers, oxy furnaces, and fluidized combustion beds (FBC or circulation dry scrubber) in power plants and industries to control pollution, reducing the sulfur content of the fuel by using scrubbers such as lime injection multi-stage burning (LIMB) and flue gas desulfurization (FGS) (Ahmadi 2020 ). The use of selective catalytic reduction process (SCR), electrochemical reduction, selective non-catalytic reduction (SNCR), and wet scrubber to reduce NOx emission (Gholami et al. 2020 ) were other control measures adopted to reduce acidic components in the emission. The expansion of renewable energy capacities (sources), such as hydroelectric projects, solar cells, nuclear power, windmills, and biofuels, for the production of electricity was enhanced instead of dependency on coal (Mohajan 2018 ). In India, vehicular emission is one of the prime contributors leading to the worsening of the air quality of cities (WHO 2018 ). Steps taken to tackle the emissions are switching to low sulfur fuel (10 ppm) and implementing Bharat VI standards for engines; the introduction of a National Automobile Scrappage Policy ( 2021 ) which ensures fleet modernization; increasing the distribution of electric and hybrid vehicles; and use of anti-smog guns and smog towers which helps to reduce pollution in the atmosphere.

This review focuses on the prevailing trend of decrease in pH of rainwater in the world and India as compared to earlier decades ago and the effects of AR on plant growth characteristics, its physiology, biochemistry, gene regulation, and soil system.

Methodology

For the literature survey, 180 papers were selected for relevant information by browsing the World Wide Web, PubMed, Google Scholar, and ResearchGate. For finding related papers, keywords such as acid rain, acidic deposition, simulated acid rain, emission from agriculture, effects of acid rain on plants, acid rain and reproductive organs, fertilizers, and acidic soil, were used. Finally, 150 articles published from August 1980 to October 2021 were considered. Data from Global Energy and CO 2 Status Report, Central Pollution Control Board (CPCB), World Energy Outlook, etc. were also used.

Acid Rain Formation

Uncontrolled emissions of SO 2 and NO x from various sources are the main constituents leading to AR. The emitted pollutants dissolve in atmospheric water vapor and turn into acids like H 2 SO 4 and HNO 3 . The interaction of SO 2 , NO x , and O 3 in the atmosphere leads to many chemical reactions which finally form H 2 SO 4 and HNO 3 mists (Calvert et al. 1985 ). Figure  1 depicts the schematic representation of the pathway of AR formation and consequent effects.

Schematic representation of the pathway of acid rain formation and consequent effects

Poor quality coal contains 0.5% of sulfur (S) with 35–40% of ash, which gets emitted into the environment after getting burned in thermal power plants. This converts S into SO 2 . Furthermore, it gets gradually oxidized into sulfite ion (SO 3 2− ).

However, SO 3 2− gets oxidized into SO 4 2− in the atmosphere due to the presence of NH 3 and O 3 , which finally get converted to H 2 SO 4 in clouds.

A recent study by Mallick et al. ( 2021 ) suggested a process that can increase SO 2 concentrations in the atmosphere where HOSO * can act as a source of S. The HOSO * is generated as an intermediate in the combustion condition from the oxidation of S and was found to be quite stable in the atmospheric condition. The new reaction path of HOSO * with NH 2 * has been identified which caused the in situ generation of SO 2 in the atmosphere.

Nitrogen (N) released from vehicular exhaust undergoes oxidation which after gradual oxidation turns into NO 2 . Photochemical conversion takes place which leads to the formation of different forms of oxides of N that ultimately result in the formation of HNO 3 .

The formation of AR involving O 3 is the most common reaction in the atmosphere. Photolysis of O 3 into nascent oxygen occurs which then reacts with H 2 O and forms OH − which then reacts with SO 2 and gets transformed into HSO 3 − .

Ozone plays an important role as an oxidant up to pH 5.0. In the liquid phase, H 2 O 2 is considered the most dominant oxidant for the conversion of dissolved SO 2 to H 2 SO 4 at pH range from 2 to 5 in the atmosphere, which is the main contributor for the acidification of cloudwater, fog, and rainwater (Gonçalves et al. 2010 ).

The Trend of Acid Rain Scenario

Countries like North America, Europe, and China are facing a huge number of problems due to acid rain in particular (Abbasi et al. 2013 ). The first evidence of AR was observed in the mid-nineteenth century. In 1972, United Nations held a conference in Sweden on the subject of the human environment which concluded that AR is a serious international pollution problem (Kowalok 1993 ). The pH of AR in Europe was reported to increase by 10% over the last 20 years. Presently, the acidity of rainwater in the countries of Europe such as Canada, Denmark, and Germany was observed to be between 4.2 and 4.5 whereas it was 4.8 in the USA (Abbasi et al. 2013 ). In 2018, the pH of Poland’s rainwater lies between 3.64 and 7.36 with mean values ranging between 4.52 and 6.58 (Diatta et al. 2021 ). According to Piñeiro et al. ( 2014 ), the pH of rainwater in Coruña (Spain) is found to be 5.55. The pH values of precipitation of several European countries including Austria, Belarus, Croatia, Finland, Ireland, Italy, Norway, Switzerland, and the UK were reported by Keresztesi et al. ( 2019 ) to be between 4.19 and 5.82 with a mean of 4.80. The higher concentration of acidic anions (SO 4 2− , Cl − , NO 3 − ) compared to neutralizing cations (Ca 2+ , Mg 2+ , NH 4 + ) can be considered a reason for the lower values of pH as reported.

As per US EPA ( 2013 ), the USA and Canada have decreased the near boundary activities of releases due to the implementation of the Cross-State Air Pollution Rule and litigation (CSAPR 2011) which reduced the sulfur and nitrogen deposition. This report further stated that the major decrease in the SO 2 and NO x emissions and deposition of acid is due to the implementation of programs such as the Clean Air Interstate Rule (CAIR), Acid Rain Program (ARP), and NO x Budget training Program (NBP). It was also mentioned that the present emission levels were still not acceptable, and complete recovery of acid-sensitive ecosystems is not possible in near future (Ahmadi 2020 ).

Andrade et al. ( 2020 ) identified AR as a rising issue in several major cities of Brazil such as São Paulo and Rio de Janeiro where low pH values of 3.5 and 4.0 were reported. Akpo et al. ( 2015 ) reported a pH of 5.19 in Djougou, West Africa. At present, SO 2 emissions in the western parts of the world are decreasing and the ecosystem of these regions is improving (Shah et al. 2000 ), whereas the situation in the eastern parts of the world, especially in the regions of south-central Asia, has continuously deteriorated over the years due to the growing size of the industrial sector and population boom. AR has affected around two million square kilometers in China and this area is also continuously expanding. Also, in around 44 cities in China, the pH values of rainwater lie between 3.8 and 4.5 while the mean value was around 5.6 (Sun et al. 2016 ). According to Watanabe and Honoki ( 2013 ), the mean rainwater pH was found to be 4.7–5.3 in the Mt. Tateyama region near the Japan Sea. The presence of CaCO 3 in dust particles leads to the neutralization of acidic species of rainwater. The Japan Environment Agency reported an average pH of 5.2 in the 1970s and below 4.7 in 2000 at Ryori on the Pacific coast which showed a fivefold increase in acidity (Shah et al. 2000 ). Table ​ Table2 2 shows the variations in the values of pH of various regions of the globe from 1980 to 2016.

Comparison of rainwater pH values in different regions of the world

In 2018, a World Health Organization (WHO) report has stated that many Indian cities including Kanpur, Faridabad, Gaya, Varanasi, and Patna are some of the most polluted cities around the globe in terms of air pollution. Studies on rainwater in India showed a range of pH from alkaline to acidic (Table ​ (Table3). 3 ). Metropolitan cities such as Mumbai, Delhi, Kolkata, and Chennai, as well as cities located close to industrial areas, show evidence of AR. According to data from CPCB, there was a significant 2–threefold increase in NO 2 level as compared to SO 2 from 2004 to 2020 (Table ​ (Table4) 4 ) which has led to a rise in the frequency of AR. In India, AR is often ruled out due to the abundance of alkaline particles (Ca 2+ , NH 4 + , and Mg 2+ ) in the atmosphere, but with increasing emissions from vehicles and industries, the contribution of acidic components has increased in rainwater (Bisht et al. 2015 ; Rao et al. 2016 ).

Range of rainwater pH in different parts of India

Average concentrations of SO 2 and NO 2 at different cities of India

Source: CPCB; BDL , below detection level; NA , data not available

Events of AR in India have increased since the last decade. During 1970–1990, in India, the regions with lower pH values of rainwater have been increasing gradually but AR has still not been considered a threat in the country (Sridharan and Saksena 1990). Datar et al. ( 1996 ) assessed the annual precipitation volume-weighted means of monthly collected rainwater samples from 10 Background Air Pollution Monitoring Network (BAPMoN) stations between 1973 and 1990. The study revealed that the pH of rainwater is decreasing in almost all stations but reductions in mean values were not significant (Datar et al. 1996 ) (Table ​ (Table5). 5 ). Based on sensitivity calculations done by using the RAIN-ASIA model, it was also predicted that the southeast coastal regions are considered most susceptible to AR (Foell et al. 1995 ). According to Bhaskar and Rao ( 2017 ), Global Atmospheric Watch (GAW) stations reported that the mean pH of rainwater was highest and lowest at Jodhpur and Mohanbari while the values vary from 5.25 to 6.91. During 1981–2012, all stations recorded a decrease in the mean pH of the precipitation. It was also observed that the probability of rainfall with low pH has decreased in Srinagar during 2001–2012 but in all other stations, acidic rainfall percentage has increased from 1981–1990 to 2001–2012 (Table ​ (Table5). 5 ). A rainfall of pH 3.67 has been reported from Allahabad. The mean pH value of rainwater was 5.32 during 2003–2005 at Dhanbad, the coal city of India. Singh et al. ( 2007 ) stated that this part of the country has been dealing with large quantities of suspended particulate matter due to various activities such as mining, untreated outlets from the industrial sector, loading and unloading of coal, and vehicular emissions. At Mahabaleshwar, a hill station located in Peninsular India, a study assessed that there was a significant concentration of SO 4 2− and NO 3 − ions in the samples taken during the summer monsoon between 2016 and 2017, and about 23% of the rainfall occurrences were acidic in nature (Waghmare et al. 2021).

Range of rainwater pH in different parts of India measured at BAPMoN station (modified from Datar et al. 1996 ) and GAW station (modified from Bhaskar and Rao 2017 )

Apart from inorganic acids (H 2 SO 4 , HNO 3 , HCl), organic acids (weak acids) can cause the acidity of rainwater. Organic acids (OCs) are a pervasive component of the troposphere and present in gaseous form in the atmosphere (Sun et al. 2016 ). Acetic (CH 3 COOH) and formic acids (HCOOH), as well as dicarboxylic acids such as oxalic acids (C 2 H 2 O 4 ), are most abundant in the atmosphere (Avery et al. 1991 ; Legrand et al. 2005 ). Yearly, in the extratropical northern hemisphere, carboxylic acid accounts for < 25% of rainwater H + , 50% in the southern tropical continents, and around 25 to 50% in the southern hemisphere, causing the rainwater pH below 4.5 (Shah et al. 2000 , 2020 ). It was estimated that the presence of these compounds in urban environments leads to 16 to 35% of the free acidity in rainwater and 65% in remote areas (Paulot et al. 2011 ).

Avery et al. ( 2006 ) reported different types of OCs in the rainwater of North Carolina, USA. Formic and acetic acids were the most abundant which comprised approximately 75% of total OCs. The presence of OCs is also reported in marine areas of Puerto Rico of the Caribbean Sea (Gioda et al. 2011 ). The sources of OCs can either be direct or indirect which include incomplete combustion of fuels in vehicles, biomass burning, biofuels, fossil fuel, and vegetation, or formed in the atmosphere by photochemical reactions. A study by Cruz et al. ( 2019 ) reported that on average, 89% of acidity in the Brazilian city Salvador was caused by OCs (48% of acetic acid and 41% of formic acid) in contrast to 11% by inorganic acids. A study of rainwater chemistry carried out in Spain by Peña et al. ( 2002 ) reported that formic and acetic acids are dominant carboxylic acids in rainwater and led to 90 and 89% of acidity while oxalic and citric acids were present in lower percentages. A study carried out by Sun et al. ( 2016 ) in the area of Mount Lu in south China showed a significant amount of OCs in rainwater which contributed to 17.66% acidity. Kumar et al. ( 2014 ) suggested that the presence of OCs led to an increase in the acidity of rainwater in Delhi. Khare et al. ( 1997 ) reported the presence of aldehyde (HCHO), formic, and acetic acid in rainwater was reported during the monsoon period at a rural site in Agra.

The Annual Trend of SO 2 and NO 2 Concentrations Across the World

SO 2 and NO 2 concentrations depict significant spatial variations throughout the world. Higher percentage changes were recorded from tropical and subtropical countries including India, Bangladesh, Pakistan, and Thailand (Table ​ (Table6). 6 ). Variations in SO 2 and NO 2 levels depend on sources and prevailing local, regional, and global meteorological conditions (Swartz et al. 2020 ). Krotkov et al. ( 2015 ) examined the long-term (2005–2015) spatial and temporal trends of SO 2 and NO 2 pollution around the globe by retrieving data from the satellite-borne Ozone Monitoring Instrument (OMI) of NASA’s Aura satellite. It was reported that in many regions, pollution levels showed dramatic upward and downward trends while others showed opposite trends of SO 2 and NO 2 . The period of 2005–2015 evidenced a drastic decrease in SO 2 and NO 2 levels in the eastern USA by 80 and > 40%, respectively, as a result of stricter emission regulations and technological advancements. Similarly, as per the data of EEA (European Environment Agency 2013 ), ~ 80% reduction in SO 2 emissions was observed in Europe during 1990–2011. Between 1980 and 1990s, a remarkable reduction of SO 2 emissions was recorded in western European countries after which SO 2 levels dropped below the detection limit of the OMI, while insignificant changes have been reported for NO 2 on a regional level (Krotkov et al.  2015 , 2016 ).

Spatio-temporal variations in the annual concentration of SO 2 and NO 2 (in terms of percentage change) in different countries

ns , not significant; NA , not available

+, increase; −, decrease

Swartz et al. ( 2020 ) assessed the long-term inter-annual and seasonal trends of atmospheric O 3 , SO 2 , and NO 2 for 21 years at the Cape Point Global Atmosphere Watch (CPT GAW) station, South Africa. The analysis revealed a constant trend of NO 2 and SO 2 concentrations for long-term average (1995–2015); however, a nominal decrease was noticed in SO 2 levels between 1995 and 2004 and then a steady rise from 2005 to 2009. The annual average concentrations of NO 2 declined from 1996 to 2002 after which a consistent increment was observed with maximum concentrations in 2011 (Swartz et al. 2020 ).

Although being the world’s most severe SO 2 polluter, the North China Plain (NCP) experienced a decreasing trend of SO 2 since 2011, with about a 50% reduction from 2012 to 2015. In contrast, NO 2 peaked in 2011, after a substantial increase of ~ 50% since 2009, which further showed a reduction of 40% between 2014 and 2015 due to the stagnant economic growth (Krotkov et al.  2015 , 2016 ). Similarly, a study by Zhao et al. (2021) reveals that the annual average concentrations of SO 2 and NO 2 throughout China decreased by 67.9 and 24.9%, respectively, in 2019 as compared to 2014. On contrary, from the period 2005 to 2015, India experienced escalating levels of SO 2 and NO 2 of more than 100 and 50%, respectively, emitted from fossil-fuelled power plants and smelters (Krotkov et al. 2015 , 2016 ). However, a significant reduction in the annual mean concentration of SO 2 in 2020 (approx.7–8%) was observed as compared to 2010–2020. This change was evident due to the COVID-19 pandemic-led national lockdown and the shutdown of industries as well as the implementation of effective control technologies such as the flue gas desulfurization (FGD) and scrubber (Kuttippurath et al. 2022 ).

Irie et al. ( 2016 ) investigated the annual trend analysis of NO 2 levels in East Asia and found that in Japan, NO 2 levels decreased from 2005 to 2013 including a larger decrease that tended to occur in metropolitan areas of Tokyo and Fukuoka. However, the NO 2 level increased by ~ 13% year −1 from 2013 to 2015. As per the observation of Ito et al. ( 2021 ), a significant reduction in (~ 75%) SO 2 concentrations has been detected in Japan over 30 years (1990–2018). Jang et al. ( 2017 ) observed an increasing trend of SO 2 levels in the rural and commercial sites of Busan, South Korea, throughout the period from 2005 to 2014 due to local emissions from shipping industries, while NO 2 levels remain constant.

The Annual Trend of Rainfall pH

A comprehensive assessment of rainwater chemistry between 1978 and 2017 collected from proximal areas of the USA showed that 87.90% of samples have an acidic composition with pH values under 5.6, including 49.12% of pH values ranging between 3.04 and 5, while 34.97% and 15.91% of the pH values were between 5–5.6 and > 5.6, respectively (Keresztesi et al. 2020 ). European countries also recorded acidic to slightly acidic pH of rainwater ranging from 4.19 to 5.82 over two decades (Keresztesi et al. 2019 ). In a long-term analysis of precipitation from 2018 to 2022 at Mt. Lushan located in South China, the pH of rainwater ranged from 4.9 to 7.9, having values of 5.8 as the annual volume-weighted mean pH of 87.7% of rainwater (Li et al. 2022 ). The study also recorded an increasing trend in the annual flux of wet deposition during the entire experimental period with 3 times higher wet flux of nitrate (76.3 kg/ha/year) than the annual wet deposition flux of sulfate (21.7 kg/ha/year), indicating that acidic deposition is still a serious environmental issue in the region. Similarly, the period 2000–2018 marked a significant increase in the pH of annual mean precipitation from 4.96 in 2000 to 6.88 in 2018 across the western Pearl River Delta region, south China (Liu et al. 2021). The annual mean pH of precipitation for 20 years (1994–2013) at Fushan Experimental Forest, northeastern Taiwan, was 4.62 ± 0.62, having ~ 77% of the rainwater considered acidic with a pH of 5.0 (Chang et al. 2017 ). Itahashi et al. ( 2021 ) reported an increase in the annual mean pH of precipitation from 4.7 to 4.8 between 2000 and 2011 at the WMO-GAW station, Ryori, northeastern Japan.

Effects of Acid Rain on Plants

Growth and yield.

Acid rain causes deleterious effects on the agricultural ecosystem by retarding the growth of crops and affecting their production (Singh and Agrawal 2004 ). It has been well established that as compared to woody plants, herbaceous plants are more sensitive to direct injury by AR (Heck et al. 1986 ). As compared to monocotyledons, dicotyledons are more sensitive toward AR (Evans 1988; Knittel and Pell 1991 ). Anatomical alterations produced by AR are modification in the thickness of cuticle (Cape 1986 ), loss of trichomes in the epidermis, cellular deformation, collapse of the mesophyll cell, occlusion of stomatal cells, and the formation of scar tissue (Da Silva 2005 ). The detrimental effects of simulated acid rain (SAR) on morphology include chlorosis, necrosis, dehydration, wilting, early senescence, stunting, pathogen infection, and death (Fig.  2 ) (Milton and Abigail 2015 ). A study by Milton and Abigail ( 2015 ) investigated the impact of SAR on the morphology of okra at pH 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, and 7.0 (control) from seed to maturity. It was found that plants wilted when SAR of pH 1.0 was applied. Yellow coloration and early leaf senescence were observed at pH 2.0. At pH 3.0, plants exhibited mild and marginal chlorosis while at pH 4.0 and 6.0 chlorosis, black spots and white powdery growth all over leaves due to fungal infection were found.

Underground regulation of soil microbes and fungi and effects on plant growth under AR stress: a high acidity, b moderate acidity. Abbreviations—(1) downregulation of the soil microbial community structure, decrease in the abundance of soil nitrogen-fixing bacteria, and decelerating the soil nutrient mineralization; (2) increase in mycorrhizal fungi which helps in remediation of heavy metals; (3) promoting pathogen infection, changing root physiological conditions; PM, plasma membrane; Ca 2+ , calcium ion; Mg 2+ , magnesium ion; Al 3+ , aluminum ion

The deleterious effects of AR have been reported on several agricultural and horticultural crops such as broad bean (Singh et al. 1992 ), tomato (Debnath et al. 2020 ), soybean (Pham et al. 2021 ), maize (Papova et al. 2019 ), spinach, bush bean, radish (Hosono and Nouchi 1993 ), and wheat (Singh and Agrawal 1996 , 2004 ). Haruna et al. ( 2016 ) found that the SAR caused severe symptoms on leaves of papaya ( Carica papaya ), and small lesions were observed after the second spray of SAR of pH 4.5. However, after the 5th and 8th spray, broad lesions, big necrotic spots on the lamina, and marginal necrosis appeared on the leaves at pH levels 4.5, 5.0, and 5.5 respectively.

A study by Andrade et al. ( 2020 ) evaluated the effects of SAR on the leaf blade surface of Joannesia princeps , a tree species of rainforest. It was found that when the seedlings were subjected to SAR of pH 4.5 (H 2 SO 4 ) compared to pH 6.0 (control), microstructural damage was detected only in the youngest leaves, which led to wilting of epidermal cells. Structural alterations in stomatal guard cells were also recorded. Rodríguez-Sánchez et al. ( 2020 ) found that when two tree species Liquidambar styraciflua and Fraxinus uhdei were exposed to SAR of pH 2.5, 3.8, and 5.6 (control), visible leaf damage and cuticle alteration were only found at pH 2.5 in both the species.

Neufeld et al. ( 1985 ) examined the effects of foliar applications of SAR of pH 2.0, 3.0, 4.0, and 5.6 on seedlings of four deciduous tree species native of the eastern USA ( Liriodendron tulipifera , Liquidambar styraciflua , Platanus occidentalis , and Robinia pseudoacacia ). SAR-induced foliar damage was only found at pH 2.0. P. occidentalis was found to be the most sensitive and L. tulipifera was the least, whereas old leaves of both species showed more damage than young leaves. Da Silva et al. ( 2005 ) screened the response of the tropical tree species ( Gallesia integrifolia , Genipa americana , Joannesia princeps , Mimosa artemisiana , Spondias dulcis ) under SAR treatments of pH 3.0 and 6.0 (control) by evaluating foliar injury, growth, and anatomical alterations in the leaves. It was found that all species showed chlorosis, necrotic spots, and curling of leaf blade after the first application of SAR, but J. princeps was found to be the most sensitive and S. dulcis was the least for foliar injury and seedling growth. In most sensitive species, necroses showed accretion of phenolic compounds, hypertrophy, and collapsed cells (Da Silva et al. 2005 ).

A pioneering study by Evans and Lewin ( 1981 ) established a relation between rainfall acidity and plant response which predicted the overall impact of the ambient level of AR on yield or productivity. Evans et al. ( 1982 ) studied the effects of different concentrations of SAR (pH 2.7, 3.1, 4.0, and 5.7) on the yield of alfalfa ( Medicago sativa ), garden beet ( Beta vulgaris ), kidney bean ( Phaseolus vulgaris ), and radish ( Raphanus sativus ). It was found that there were no significant differences observed in root mass of radish, kidney bean, and alfalfa, while a significant reduction in yield of beetroot was observed at SAR of pH 2.7, 3.1, and 4.0. The SAR treatments caused reductions in plant growth and yield of corn (Banwart et al. 1988 ), coriander (Dursun et al. 2000 ), green pepper (Shripal et al. 2000 ), pinto beans (Evans and Lewin 1981 ), and soybean (Evans et al. 1981a , b ). A control field experiment using greenhouse chambers was conducted to determine the effect of SAR of sulfuric acid rain of pH 3.0, 3.5, 4.0, and 5.6 (control) on the yield of several crops such as beet, broccoli, carrot, cabbage, cucumber, radish, mustard greens, spinach, tobacco, cauliflower, potato, green pea, peanut, soybean, alfalfa, red clover, strawberry, tomato, green pepper, onion, corn, wheat, oats, barley, orchardgrass, bluegrass, ryegrass, and timothy (Lee et al. 1981 ). It was found that marketable yield production, i.e., total aboveground portion and root weight, was inhibited in the case of beet, carrot, radish, mustard greens, and broccoli while stimulated for alfalfa, green pepper, orchardgrass, tomato, strawberry, and timothy when exposed to pH 3.0–4.0. Potato yield was also inhibited at pH 3.0 while stimulated at pH 3.5 and 4.0. No significant effects on the yield of other crops were reported. Similar results found in tomato when treated by SAR treatment of pH 2.5 showed that the growth parameters including plant height, the number of leaves, shoot weight, and stem girth were reduced significantly (Debnath et al. 2020 ).

Singh and Agrawal ( 1996 ) conducted a field experiment on two cultivars of wheat ( Triticum aestivum  var. Malviya 206 and 234) to assess the effects of SAR of pH 5.6 (control), 5.0, 4.5, 4.0, and 3.0. It was found that leaf area, shoot and root lengths, total biomass, no. of grains per plant, grain weight per plant, and yield m −2 were decreased significantly at all levels of SAR as compared to control. Similar results were observed when two different cultivars of wheat (Malviya 213 and Sonalika) were applied with SAR of pH 5.6, 5.0, 4.5, 4.0, and 3.0. The reduction in yield of Malviya 213 is observed at pH 3.0 and 4.0, whereas only at pH 3.0 in Sonalika as compared to control (Singh and Agrawal 2004 ).

One of the important forages used in China, Lolium perenne , when exposed to SAR of different pH 7.0, 6.0, 5.0, 4.0, 3.5, and 3.0, showed increments in the root-shoot ratio and total biomass between pH 4.0 and 7.0 with the maximum value at pH 5.0, indicating that moderate acidity promoted the growth of leaves, while strong AR impaired the leaves and suppresses the growth of seedlings (Yin et al. 2021 ). The growth decreased below pH 5.0, with the greatest reduction occurred at pH 3.5. Several studies have also reported that the low acidity of rain improves seed germination, promotes the aboveground biomass, and increases overall biomass accumulation in the plants (Ramlall et al. 2015 ).

Pham et al. ( 2021 ) exposed soybean ( Glycine max ) plants to SAR of pH 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0 (control). It was found that SAR of low pH decreased the germination rate, leaf area index, shoot length, and the number of main branches of the plants. The components of yield and actual yield also decreased especially in the plants treated with pH 3.0. A similar result was obtained in Manihot esculenta when subjected to SAR of pH 2.0, 3.0, 4.0, 5.0, 6.0, and 7.0 (control) (Odiyi and Bamidele 2014 ). It was found that high acidity of SAR (pH 2.0 and 3.0) led to the significant reduction of plant height, leaf area, total biomass, relative growth rate (RGR), and the harvest index (HI) (Odiyi and Bamidele 2014 ).

SAR induced browning of leaves, with 70% leaf abscission in Vigna unguiculata when exposed to SAR of pH 2.0, 3.0, and 4.0 as compared to pH 7.0 (control) (Odiyi and Eniola 2015 ). The RGR and HI were lowest compared to pH 7.0. Liang et al. ( 2015 ) reported that SAR at pH 5.5 did not affect the RGR of rice seedlings as compared to the control. However, the maximum decrease of 79 and 57% in RGR of seedlings was observed when exposed with SAR of pH 3.5 and 2.5.

AR affects the plants either by damaging the foliage leading to a reduction in canopy cover and their growth or increasing susceptibility to drought as well as diseases (Aber et al. 2001 ). Acidic deposition impacted eastern USA red spruce and sugar maple through loss of Ca from cell membrane due to direct leaching from foliage or reduction in uptake of Ca from soil or due to losses of available Ca and Mg which made the trees more susceptible to winter injury. The Black Forest in Germany and Bavaria, Poland, the Czech Republic, and Switzerland are the areas in Europe most vulnerable under AR. Similar reports of a decline in the health of pine species have been reported in Asia (Driscoll and Wang 2019 ). Asian pine species suffered negative effects due to soil acidification which results from nutrient inequality caused due to high Al and low Ca in soil (Driscoll and Wang 2019 ).

A field investigation on the seedlings of four tree species from south China ( Cunninghamia lanceolata , Fokienia hodginsii , Phoebe zhennan , and Pinus massoniana ) revealed that SAR of high acidity (pH 2.5) significantly reduced the germination of F . hodginsii and P . zhennan , while SAR of pH 2.5, 3.5, 4.5, and 5.5 increased the germination of P . massoniana and had no effect on the germination of C . lanceolata seeds (Gilani et al. 2021 ). The results further demonstrated that seedling germination is more resistant than seed emergence, and seed germination in conifer species is less sensitive under SAR of pH 4.5 and 5.5 as compared to broad-leaved species. As a whole, AR of pH 3.5 was found to be the threshold level, and below this value, detrimental effects on seed germination and seedling emergence were recorded (Gilani et al. 2021 ). In contrast, Lee and Weber ( 1979 ) found that SAR of pH 2.3 to 4.0 promotes seedling emergence and growth of woody tree species (Fig.  2 b).

In nature, plants are rarely exposed to anyone kind of stress. Invasion by alien plant species causes a significant effect on the ecosystem. An experiment performed by Cheng et al. ( 2021 ) using four Asteraceae alien invasive plants (AIP), i.e., Conyza canadensis , Erigeron annuus , Aster subulatus , and Bidens pilosa , on germination of Lactuca sativa revealed that SAR of high acidity (pH 4.5) increases the process of invasion and allelopathy on the germination and root length of L. sativa.

Physiological and Biochemical Performances

Plant’s various physiological and biochemical traits were found to be negatively damaged by AR (Lee et al. 1981 ). The photosynthetic pigments in plants are most sensitive to air pollutants and are also identified as an indicator of the physiological status of plants stressed by AR. As shown in Table ​ Table7, 7 , different plants responded differently to acid deposition, but there was a common response of reduction in foliar chlorophyll content of different plant species under SAR treatments. Likewise, AR hampered the photosynthetic activity; nonetheless, the effects of SAR on photosynthetic activities varied depending on the plant species, stage, pH of the acid rain, and environmental conditions (Tong and Zhang 2014 ). Copolovici et al. ( 2017 ) showed that the photosynthetic parameters including stomatal conductance and assimilation rate of Phaseolus vulgaris decreased drastically when sprayed with acidic solutions of pH 4.0 and 4.5. Assimilation rate recovered at the initial values after 2 h of treatments, while stomatal conductance increased as acidity increased. Similarly, Odiyi and Eniola ( 2015 ) reported that in Vigna unguiculata (cowpea) leaves, SAR of pH 2.0 and 3.0 leads to reduced chlorophyll content as compared to the pH 7.0 (control).

Effects of acid rain on growth and biochemical traits of plant species

The maximal photochemical quantum efficiency of Photosystem II (PSII) represented by Fv/Fm is widely used as a sensitive stress indicator of photosynthetic performance in plants. The decline in Fv/Fm in plants indicates an increase in non-photochemical quenching processes or photo-inactivation of PSII reaction centers (Liu et al 2018b ). In rice, when leaves are subjected to SAR of pH 3.5 and 2.5, it was found that Fv/Fm showed reductions but did not show any difference at pH 5.5 from control (Wen et al. 2011 ). It indicates that the extremely high acidity SAR not only affects photosynthetic components but destroys chloroplast structure (Wen et al. 2011 ).

Sun et al. ( 2016 ) studied the impact of AR on chloroplast and its ultrastructure, photosynthesis, ATP synthase activity, gene expression, intracellular H + level, and water content of rice seedlings. It was found that at pH 4.5, 4.0, or less, chloroplast structure remained unchanged but got destroyed. It was also reported that SAR of pH 4.0 or less decreased the leaf water content, inhibits the expression of chloroplast ATP sythase subunits which caused decreased activity of chloroplast ATP synthase, reduced photosynthesis, and damage the integrity of chloroplast structure, while at pH 4.5, the expression of ATP synthase subunits and activity got increased and promoted. It shows that AR influences the plant growth and development by changing the acidity of the cells which in turn affects the chloroplast ATPase transcription and net photosynthetic rate.

Foliar application of SAR of pH 3.0, 3.5, 4.0, 4.5, 5.0, and 5.5 on green leaves of 13 deciduous species ( Acacia , Acer , Betula spp., Carpinus betulus , Castanea spp., Fagus , Juglans sp., Malus domestica , Populus , Quercus robur , Salix , Tilia europaea , Ulmus minor ) and 10 species of dicotyledonous plants ( Bellis perennis , Beta vulgaris , Brassica oleracea , Cucumis sativas , Lactuca sativa , Lycopersicon esculentum , Phaseolus spp., Petroselinum crispim , Solanum tubersum , Vitis ) resulted into leaching of Ca, Mg, Fe, and Zn from the photosynthetic organs (Diatta et al. 2021 ). Intra-species variations were found in deciduous trees and dicotyledonous plants with more pronounced leakage of alkaline elements (Ca, Mg) and Zn. It was found that 77% of deciduous species showed very low to intermediate photosynthetic recovery implying that highly AR impacted trees have lower survival whereas, and dicotyledonous plants showed 70% (high to very high) survival. Mineral nutrients particularly Ca and Mg increased plants’ resistance to AR (Diatta et al. 2021 ). Zhou et al. ( 2020 ) found that SAR of pH 2.5 and 3.5 severely damaged the root plasma membrane (PM) permeability in Masson pine ( Pinus massoniana ) seedlings, while pH 4.5 and 5.6 lowered the PM permeability, thus indicating that SAR can destroy the integrity of plant PM.

Effect of AR on Plants at the Genetic Level

A recent study by Raju et al. ( 2021 ) on Allium cepa roots revealed that SAR of sulfuric acid of pH 3.8, 4.08, and 4.4 showed adverse effects on the morphological aspects of root and altered the root cells genetically compared to pH 4.63, 5.32, and 7.0. The SAR of sulfuric acid of pH 3.8 and 4.08 led to low root growth which is accompanied by a shorter root length in comparison with pH 7.0. Table ​ Table8 8 shows the mean root length and numbers of roots grown under different pH of SAR. It was found that the SAR of sulfuric acid of lower pH values (pH 3.8) significantly decreased the number of cells in prophase, metaphase, anaphase, and telophase, thus restraining cell division which led to lower mitotic index, causing the chromosome reorganization and thus led to modification in the number or structure of chromosomes. The chromosomal aberrations such as chromosomal bridges and fragments, nuclear lesions, micronucleus, polyploidy, binucleated nucleus, vagrant chromosomes, and sticky chromosomes were also recorded.

Shows the means for length (cm), numbers of roots grown, and decline of mitotic index in different pH values of SAR (modified from Raju et al. 2021 )

A proteomic study on Arabidopsis thaliana using 2-D gel electrophoresis revealed that several genes that are involved in the light reaction of photosynthesis such as photosynthetic electron transport chain-related genes and light-harvesting complex in photosystem I (PSI)- and PSII-related gene were repressed, while genes related to cell defense were upregulated under SAR (Liu et al. 2013 ). A study on Camellia sinensis using transcriptomic analysis reported the expression of multiple genes associated with photosynthesis, N, and S, and carbohydrate metabolisms were altered under SAR treatments (Zhang et al. 2020 ). A total of six genes that are involved in light reactions are repressed which include two genes encoding the protein of the light-harvesting complex of PSII, two genes involved in the PSII subunit, and one of PSI subunit and of ferredoxin-NADP ( +) reductase (FNR). This suggests that SAR directly damages the leaves, thus disturbing the light-harvesting and electron transfer process of PSI and PSII which in turn decreases the carbon assimilation efficiency of plants (Zhang et al. 2020 ). Genes involved in metabolism pathways of starch and sucrose as well in glycolysis such as phosphoglycerate kinase gene (PGK3), pectin methylesterase genes (PMEPCRA), enolase gene (LOS2), phosphoglycerate dehydrogenase gene (EDA9), and amidophosphoribosyl transferase gene (ASE2) were downregulated under high acidic treatment of pH 2.5.

Debnath et al. ( 2020 ) analyzed the transcriptomic profile of greenhouse-grown tomato plants exposed to SAR of pH 2.5 and 5.6 (control) and found that 182 genes were upregulated, while 1046 genes were downregulated and 17,486 genes showed no differential expression. The qPCR results used 15 genes to confirm the consistency and reliability of the profile, and among these genes, 11 genes which are related to plant secondary metabolites and 4 genes related to stress-responsive including bZIP, ERF, MYB, and WRKY family protein got downregulated in treated plants (Debnath et al. 2020 ).

A recent study by Yang et al. ( 2018 ) on soybean seedlings by using the next-generation sequencing platform has identified 416 genes that are related to the regulation of N, S, and photosynthesis, and carbohydrate metabolism showed alteration in expression when exposed to SAR. Moreover, different transcription factors that are related to abiotic and biotic stress such as WRKY, zinc finger proteins, MYB, and Ca signal pathway-associated genes were induced after SAR treatment (Liu et al. 2013 ).

Effects of Acid Rain on Soil

Being dynamic and complex in nature, soil can be easily affected by AR, which results in soil acidification and an increase in the exchange between H + and nutrient cations (Mg, K, and Ca) in the soil and results in leaching (Breemen et al. 1984 ). The growth of plants and soil fertility are affected indirectly by deficiency of these nutrients (Mishima et al. 2013 ). Nutrient deficiency inhibits nodulation in plants by limiting legumes’ ability to transmit signals that attract the rhizobia (Sullivan et al. 2017 ) and indirectly inhibits ectomycorrhizal fungal association with plants (Maltz et al. 2019 ), which results in reduced plant vigor and productivity (Fig.  2 ).

Ma et al. ( 2020 ) found that AR influenced the soil’s chemical properties under Chinese cabbage cultivation. It was observed that spraying of SAR of pH 3.5 reduced the soil pH by 0.21, 0.19, and 0.15 units at a depth of 0, 4, and 8 cm as compared to the pH 7.0 (control). However, no significant difference was found in soil pH between treatments at pH 4.5, 5.5, and 7.0. Similarly, Zhou et al. ( 2020 ) found that SAR caused a lowering of both rhizosphere and non-rhizosphere soil pH with the decrease of SAR pH in Masson pine ( Pinus massoniana ) seedlings. Wei et al. ( 2020 ) also showed that SAR of pH 5.5, 4.5, 3.5, and 2.5 reduced the soil pH by 5.1, 6.8, and 7.0% in latosols, lateritic red soils, and red soils, respectively. Soils having a high cation exchange capacity (CEC) and clay content showed more resistance to SAR at low acidity levels of pH 5.5 and 4.5. The maximum decline of soil pH has been observed in the soil having the lowest CEC and clay content under SAR of pH 2.5. Latosols are found to be more resistant to AR and lateritic red soils are the least as the lateritic red soil contains the lowest soil CEC and clay content. The CEC of soil mainly rely on various physical, chemical, and biological properties of soil such as soil pH, clay, and soil organic matter, which helps to mitigate the effects of acidity on the soil. Pedogenic acidification also affects water holding capacity, porosity, and soil structure (Yadav et al. 2020 ). Furthermore AR composition also has an immense impact on soil chemical and biological properties.

AR negatively regulates litter decomposition and soil respiration (Mo et al. 2008 ), but hardly affects soil temperature and soil moisture (Wu et al. 2016 ). It was reported that SAR of pH 2.0, 3.0, and 4.0 decelerates the litter decomposition in birch, spruce, and pine (Francis 1982 ). The deposition of N is suggested to be one of the key drivers of C storage in the forest (Wei et al. 2012 ). The increase in the amount of N deposition could increase sequestration of soil C by suppressing the decomposition of litter and soil organic carbon (Frey et al. 2014 ), and can decrease soil microbial biomass C. AR increases dissolved organic carbon in soil (Fang et al. 2009 ). Wu et al. ( 2016 ) reported an increase in soil total organic carbon in topsoil (upper 10 cm) by 24.5% at SAR treatment of pH 3.0 compared to pH 4.5. Tang et al. ( 2019 ) also found that litter decomposition significantly decelerated in needle of Cunninghamia lanceolata and leaf of Cinnamomum camphora under AR treatments.

A study reported that SAR treatments of pH 2.5, 3.5, 4.5, and 6.4–6.6 (control) on C. sinensis (tea) cultivated on red soil decreased the levels of both available soil Mg and Ca, while SAR of pH 2.5 leads to increase in ratios of Al/Mg and Al/Ca, but decrease N/Al in twigs and roots (Hu et al. 2019 ). When SAR of pH 3.0 along with earthworm and mycorrhizal fungi (MF) treatments were applied on seedling of maize, significant increments in shoot biomass, nutrient uptake, an abundance of functional nitrogen-fixing bacteria, activation of soil nutrients, and promotion of transfer to the root system were found (Wang et al. 2021 ). The study also suggests that soil acid-neutralizing capacity can be improved by the use of earthworm and MF which helps them to combat the low pH levels (Fig.  2 ) (Wang et al. 2021 ).

AR has a severe effect on the activity, mobility, and environmental behavior of heavy metals (HMs) (Hernandez et al. 2003 ). AR after falling on the ground may lead to the release of HMs from soil and thus alters the soil chemical status, groundwater contamination, and function of the decomposer community (Ding et al. 2011 ). Kim et al. ( 2010 ) reported that under acidic conditions, HMs such as Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn become more soluble and mobile. Accumulation of HMs in the soil also affects its fertility by forming ion complexes with toxic metal ions such as Al 3+ , Pb 2+ , Hg 2+ , and Cd + (Ling et al. 2010 ). AR leads to an increase in levels of soluble Ni as well as Zn in soil except of Cu, Cd, or Pb as they are considered to interact with organic matter (Merino et al. 1994 ).

An increase in soil acidity also enhances the extractable aluminum (Al 3+ ) in the soil leading to Al toxicity (Hu et al. 2017 ). Mannings et al. ( 1996 ) reported that low acid treatments of pH 5.6 and 4.0 caused increased mobilization of Al and Zn in soil, while Cu, Mn, and Pb were observed only at high acid treatments of less than pH 2.5.

Li et al. ( 2015 ) found that SAR of pH 4.0 resulted in the release of HMs in the soil in decreasing order of Cd > Zn > Cu > Pb. In addition, HMs released after AR leaching was strongly associated with HM speciation and soil properties such as pH, texture, and organic matter. Ma et al. ( 2021 ) reported a significant reduction in the total concentration of Pb and Zn in soil when treated with SAR of pH 3.0, 4.0, and 5.6. The study revealed that high acidity contributes to the release of soil colloidal particles, and significantly enhanced the mobilization of Pb and Zn in soils due to the formation of organic–inorganic complexes with colloidal particles that are covered with organic matter, oxides of Fe and Al, and microbial cells in soil, which provide strong adsorption surface to these metal ions (Sen and Khilar 2006 ). Kim et al. ( 2010 ) studied the effects of SAR of pH 3.0, 4.5, and 5.6 on the transfer and phytoavailability of HMs in soil collected from a paddy field near a smelter in China. It was found that phytoavailability of HMs was strongly controlled by the pH of AR and lower pH can elevate the plant uptake of HMs, except Pb. After SAR treatments, total HM concentrations in soil were increased twice under pH 3.0 compared to pH 5.6. The concentrations of Cu and Zn were highest at pH 3.0 and lowest at pH 5.6. However, Cd was found to be highest and lowest at pH 4.5 and 5.6 respectively. In the case of Pb, decreasing acidity led to increased availability in exchangeable and carbonate forms because Pb changed to an available phase only after desorption with strong acid.

AR causes changes in the micro-environment of the soil, thus resulting in inhibition of the soil micro-organism activities and enzymes of soil nutrient cycling which in turn negatively affects the conversion efficiency of soil nutrients such as N, P, and S (Wang et al. 2018 ). Killham et al. ( 1983 ) reported that when the Sierran forest soil planted with Ponderosa pine seedlings were sprayed with SAR of pH 2.0, 3.0, 4.0, and 5.6, changes in microbial activity were most significant in surface soil. Soil respiration, dehydrogenase, and microbial activity were simulated under pH 3.0 and 4.0, while SAR of pH 2.0 shows inhibition of respiration and enzymatic activities. Soils receiving SAR of pH 3.0 showed increased arylsulfatase and decreased phosphatase activity, while urease was unaffected (Killham et al. 1983 ). Sinsabaugh et al. ( 2010 ) reported that AR affects soil hydrolase activity, while the activity of phosphatase shows an increasing trend with decreasing soil pH.

Effect on Soil due to Transition in Composition of AR

As the chemical composition of rainwater has been gradually changing, the shifting of AR from sulfuric to mixed and then nitric type has impacted soil enzymatic activity and microbial biomass differently (Li et al. 2021 ). When 2-year-old seedlings of Cunninghamia lanceolata , Cyclobalanopsis glauca , Pinus massoniana , and Phyllostachys edulis were exposed with SAR of sulfuric acid (S/N = 5), mixed acid (S/N = 1), and nitric (S/N = 0.2) acid of pH 2.5, 3.5, and 4.5, it was found that enzymatic activities decreased significantly under high- and mild-intensity AR treatments, and were lower than that under pH 7.0 (control). At lower acidity of all treatments, the soil rhizosphere enzyme activity was higher as compared to the control. The activity in P. massoniana , C. lanceolata , and P. edulis was inhibited more by nitric acid, while C. glauca was more inhibited by sulfuric acid (Li et al. 2021 ). Liu et al. ( 2020 ) also found that the activities of phosphatase, sucrase, and urease were higher under nitric acid as compared with sulfuric acid. Moreover, Liu et al. ( 2017 ) reported that increasing acidity of sulfuric acid (pH 3.5, 2.5) and nitric acid (pH 3.5, 2.5) leads to a decline in soil pH as compared to the pH 6.6 (control). However, no significant difference was observed among the same acidity of sulfuric and nitric acid.

Lv et al. ( 2014 ) found that a decrease of SO 4 2− /NO x − in the AR led to decrease of soil pH. The soil pH of the broad-leaved forest showed significant reduction only under mixed and nitric acids (S/N = 0:1), while the coniferous forest showed a decrease in soil pH in all AR types. Under nitric acid treatment, most soil enzyme activities except phosphatase were significantly lower than that in mixed acid (S/N = 5:1, 1:1, 1:5) and sulfuric acid (S/N = 1:0). The negative effects of nitric acid were more pronounced than those of sulfuric and mixed acid. The results revealed that the SO 4 2− /NO 3 − ratio in AR is an important factor that has a profound impact on litter decomposition, soil microbial biomass, and soil enzyme activities. Liu et al. ( 2021a , b ) reported that AR of different S/N ratios (sulfuric acid = 5:1, mixed acid = 1:1, and nitric acid = 1:5) did not have a significant effect on soil pH at the initial period of the experiment except for nitric acid pH 2.5. Soil enzymatic activity of urease and phosphatase was affected when subjected to AR with higher acidity. The activities of soil urease were highly intensified, and conversely, phosphatase activity decreased when exposed to nitric acid of pH 2.5.

Effects of Acid Rain on Reproductive Structures

The impact of AR is not limited to vegetative organs of the plants but also affects generative parts which include structures such as pollens and ovules. AR results in inhibition of pollen germination and pollen tube elongation and as a result affects pollination and fertilization and changes the quality and quantity of seeds (Fig.  2 ). Acidity (pH < 3.1) causes morphological alterations in pollens below pH 3.0. The pollen germination was completely stopped in apple ( Malva sylvestris ) at pH 2.9 (Munzuroglu et al. 2003 ). AR reduced the sucrose permeability in pollen (Renzoni and Veigi 1991 ). Wertheim and Craker ( 1988 ) also found a reduction in pollen germination in corn ( Zea mays ) by 25% at pH 2.6 compared to 5.6. It was shown that pollen tube length decreased in date palm and rice with an increase in acidity of rainwater (Ismail and Zohair 2013 ). Nandlal and Sachan ( 2017 ) conducted a field study to assess the effects of SAR of 7.0, 5.7, 4.5, and 3.0 on pollen germination of sunflowers which showed significant reductions of 71, 51, and 43% in pollen germination at 5.7, 4.5, and 3.0 respectively.

Microscopic studies in bean plants reported variations in the ovule’s formation, development, structure, and protein content (Majd and Chehregani 1992 ). Plants grown in pots when subjected to SAR of pH 2.0, 3.0, 4.0, and 4.5 showed a reduction in the size of the embryo sac (34%), poor penetration of embryo sac into nucellar tissue, increase in the volume of the vacuole in nucellar cells, accumulation of starch-like particles in the embryo sac, and overgrowth of ovule integuments leading to early blockage of micropyle canal (Majd and Chehregani 1992 ). Alterations in ovules resulted in abnormalities in seed formation and seed protein. The bean plants when exposed to an acidic solution of pH 2.0 set an average of 3 seeds as compared to 5–6 seeds in normal plants. There was no change in protein pattern and band numbers when seed storage protein was extracted and run on SDS-PAGE. Acidification of rain hampers gene regulation which may decrease protein production and cause modification of the quantity of protein bands (Chehregani and Kavianpour 2007 ).

Acid rain is one of the global-scale environmental challenges that have caused widespread negative effects on ecosystems during the last several decades. Gradual increase in emissions of major acid rain precursors (SO 2 and NO 2 ) in the atmosphere has resulted in view of tremendous economic development and industrial growth throughout the world. Acid rain, earlier identified as a problem of developed countries, has now spread in developing countries. The most economically developing countries like India, China, and Brazil are experiencing increased instances of AR frequency. Emission patterns of tropical and subtropical countries revealed the threats by AR are going to be more adverse in the near future as evidenced from decreasing trend of pH of rainwater. AR has potential short-term as well as long-term negative effects on plant integrity, forest and grassland ecosystems, and soil chemistry and biology. Acid rain affects plants’ biochemical, physiological, and cellular processes and causes alteration in gene expression. It enhances the chance of invasion of alien plant species through allelopathy. Soil physical and chemical properties and microbial community structure and functions are also negatively altered under AR influence.

Complications of acid rain have been tackled to some extent in the developed world by implementing the emission norms for the gases effectuating acid rain. To avoid such problems, robust and effective monitoring of emissions along with stringent regulation policies is required to be adopted by the developing world. Additionally, increasing NO x pollution around the globe changes the chemical composition of AR. A comprehensive assessment and prediction of the impacts of changing types of acid rain on plant growth and function, biodiversity, and soil properties are needed in view of scarce studies conducted on such aspects. Further investigations are also needed to assess the futuristic impacts of acid rain with a dynamically changing environment on different facets of plants and ecosystems in India and around the world which may give valuable insights into differential plant responses under AR stress.

Acknowledgements

The authors are thankful to the Head, Department of Botany, and the Coordinators, CAS in Botany, Institute of Eminence and Interdisciplinary School of Life Sciences, Banaras Hindu University, for providing necessary facilities to carry out a systematic literature review. MA is also thankful to SERB, New Delhi for providing JC Bose Fellowship.

Author Contribution

Jigyasa Prakash: conceptulization, visualization, writing original draft. Shashi Bhushan Agrawal: visualization, writing—review and editing. Madhoolika Agrawal: writing—review and editing and supervision. All authors read and approved the final manuscript.

The Council of Scientific and Industrial Research (CSIR), New Delhi, India, provided financial support in the form of CSIR-UGC JRF (file no. 09/013(0934)/2020-EMR-I).

Declarations

The authors declare no competing interests.

Publisher's Note

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Contributor Information

Jigyasa Prakash, Email: moc.liamg@uhbhsakarpasaygij .

Shashi Bhushan Agrawal, Email: moc.liamg@65lawargabs .

Madhoolika Agrawal, Email: [email protected] .

• Abbasi T, Poornima P, Kannadasan T, Abbasi SA. Acid rain: past, present, and future. Int J Environ Eng. 2013; 5 :229–272. doi: 10.1504/IJEE.2013.054703. [ CrossRef ] [ Google Scholar ]
• Aber J, Neilson RP, McNulty S, Lenihan JM, Bachelet D, Drapek RJ. Forest processes and global environmental change: predicting the effects of individual and multiple stressors: we review the effects of several rapidly changing environmental drivers on ecosystem function, discuss interactions among them, and summarize predicted changes in productivity, carbon storage, and water balance. J Biosci. 2001; 51 :735–751. doi: 10.1641/0006-3568(2001)051[0735:FPAGEC]2.0.CO;2. [ CrossRef ] [ Google Scholar ]
• Ahmadi GM. Acid rain, causes, effects and control strategies. Int J All Res Writings. 2020; 1 :219–225. [ Google Scholar ]
• Akpo AB, Galy-Lacaux C, Laouali D, Delon C, Liousse C, Adon M, Darakpa C. Precipitation chemistry and wet deposition in a remote wet savanna site in West Africa: Djougou (Benin) Atmos Environ. 2015; 115 :110–123. doi: 10.1016/j.atmosenv.2015.04.064. [ CrossRef ] [ Google Scholar ]
• Ambient air quality monitoring data for the year 2004 and 2020 (Manual Monitoring under National Ambient Air Quality Monitoring Programme) CPCB. https://cpcb.nic.in/manual-monitoring/ and http://www.cpcbenvis.nic.in/airpollution/bulletin/del/2004/maindata2004.htm
• Andrade GC, Castro LN, & da Silva LC (2020) Micromorphological alterations induced by simulated acid rain on the leaf surface of Joannesia princeps Vell. (Euphorbiaceae). Ecol Indic 116:106526 10.1016/j.ecolind.2020.106526
• Atkins DH, Irwin JG, Tuck AF, Scriven RA, Barrett CF, Cape JN, Fowler D, Kallend AS, Martin A, Pitman JI (1983) Warren Spring Lab., Stevenage (United Kingdom): Acid deposition in the United Kingdom
• Avery GB, Jr, Kieber RJ, Witt M, Willey JD. Rainwater monocarboxylic and dicarboxylic acid concentrations in southeastern North Carolina, USA, as a function of air-mass back-trajectory. Atmos Environ. 2006; 40 :1683–1693. doi: 10.1016/j.atmosenv.2005.10.058. [ CrossRef ] [ Google Scholar ]
• Avery GB, Jr, Willey JD, Wilson CA. Formic and acetic acids in coastal North Carolina rainwater. Environ Sci Technol. 1991; 25 :1875–1880. doi: 10.1021/es00023a005. [ CrossRef ] [ Google Scholar ]
• Bamidele JF, Eguagie MO. Ecophysiological response of Capsicum annuum L. exposed to simulated acid rain. Niger J Biotechnol. 2015; 30 :48–52. doi: 10.4314/njb.v30i1.6. [ CrossRef ] [ Google Scholar ]
• Banwart WL, Porter PM, Ziegler EL, Hassett JJ. Growth parameter and yield component response of field corn to simulated acid rain. Environ Exp Bot. 1988; 28 :43–51. doi: 10.1016/0098-8472(88)90045-7. [ CrossRef ] [ Google Scholar ]
• Behera S, Mishra PC, Ghosh S, Goswami C, Mallick B. Microscopic Observation of Acid Rain Induced Bacopa monnieri L. Microsc Res. 2019; 7 :11–25. doi: 10.4236/mr.2019.72002. [ CrossRef ] [ Google Scholar ]
• Bhaskar VV, Rao SP. Annual and decadal variation in chemical composition of rain water at all the ten GAW stations in India. J Atmos Chem. 2017; 74 :23–53. doi: 10.1007/s10874-016-9339-3. [ CrossRef ] [ Google Scholar ]
• Bhatti N, Streets DG, Foell WK. Acid rain in Asia. Environ Manage. 1992; 16 :541–562. doi: 10.1007/BF02394130. [ CrossRef ] [ Google Scholar ]
• Bisht DS, Dumka UC, Kaskaoutis DG, Pipal AS, Srivastava AK, Soni VK, Tiwari S. Carbonaceous aerosols and pollutants over Delhi urban environment: temporal evolution, source apportionment and radiative forcing. Sci Total Environ. 2015; 521 :431–445. doi: 10.1016/j.scitotenv.2015.03.083. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Bobbink R, Hicks K, Galloway J, Spranger T, Alkemade R, Ashmore M, De Vries W. Global assessment of nitrogen deposition effects on terrestrial plant diversity: a synthesis. Ecol Appl. 2010; 20 :30–59. doi: 10.1890/08-1140.1. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Breemen NV, Driscoll CT, Mulder J. Acidic deposition and internal proton sources in acidification of soils and waters. Nature. 1984; 307 :599–604. doi: 10.1038/307599a0. [ CrossRef ] [ Google Scholar ]
• Calvert JG, Lazrus A, Kok GL, Heikes BG, Walega JG, Lind J, Cantrell CA. Chemical mechanisms of acid generation in the troposphere. Nature. 1985; 317 :27–35. doi: 10.1038/317027a0. [ CrossRef ] [ Google Scholar ]
• Cape JN. Effects of air pollution on the chemistry of surface waxes of Scots pine. Wat Air Soil Poll. 1986; 31 :393–399. doi: 10.1007/BF00630856. [ CrossRef ] [ Google Scholar ]
• Chandravanshi CK, Patel VK, Patel KS. Acid rain in Korba city of India. Indian J Environ Prot. 1997; 17 :658–661. [ Google Scholar ]
• Chang CT, Wang CP, Huang JC, Wang LJ, Liu CP, Lin TC. Trends of two decadal precipitation chemistry in a subtropical rainforest in East Asia. Sci Total Environ. 2017; 605 :88–98. doi: 10.1016/j.scitotenv.2017.06.158. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Chehregani Abdolkarim, Kavianpour Farideh. Effects of Acid Rain on the Developmental Stages of Ovules and Seed Proteins in Bean Plants (Phaseolus vulgaris L.) American Journal of Plant Physiology. 2007; 2 (6):367–372. doi: 10.3923/ajpp.2007.367.372. [ CrossRef ] [ Google Scholar ]
• Cheng H, Wang S, Wei M, Yu Y, Wang C. Effect of leaf water extracts of four Asteraceae alien invasive plants on germination performance of Lactuca sativa L. under acid deposition. Plant Ecol. 2021; 222 :433–443. doi: 10.1007/s11258-021-01117-5. [ CrossRef ] [ Google Scholar ]
• Copolovici L, Ban A, Faur I, Copolovici D (2017) The influence of simulated acidic rain on plants volatile organic compounds emission and photosynthetic parameters. AgroLife, 73.
• Cruz LP, Mota ER, Campos VP, Santana FO, Luz SR, Santos DF (2019) Inorganic and organic acids in the atmosphere of the urban area of the city of Salvador, Brazil. J Braz Chem Soc 30:904–914. 10.21577/0103-5053.20180227
• da Silva LC, Azevedo AA, da Silva EAM, Oliva MA. Effects of simulated acid rain on the growth of five Brazilian tree species and anatomy of the most sensitive species ( Joannesia princeps ) Aust J Bot. 2005; 53 :789–796. doi: 10.1071/BT04096. [ CrossRef ] [ Google Scholar ]
• Datar SV, Mukhopadhyay B, Srivastava HN. Trends in background air pollution parameters over India. Atmos Environ. 1996; 30 :3677–3682. doi: 10.1016/1352-2310(96)00052-0. [ CrossRef ] [ Google Scholar ]
• Debnath B, Hussain M, Irshad M, Mitra S, Li M, Liu S, Qiu D. Exogenous melatonin mitigates acid rain stress to tomato plants through modulation of leaf ultrastructure, photosynthesis and antioxidant potential. Molefw. 2018; 23 :388. doi: 10.3390/molecules23020388. [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Debnath B, Li M, Liu S, Pan T, Ma C, Qiu D. Melatonin-mediate acid rain stress tolerance mechanism through alteration of transcriptional factors and secondary metabolites gene expression in tomato. Ecotoxicol Environ Saf. 2020; 200 :110720. doi: 10.1016/j.ecoenv.2020.110720. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Diatta J, Youssef N, Tylman O, Grzebisz W, Markert B, Drobek L, Lejwoda P. Acid rain induced leakage of Ca, Mg, Zn, Fe from plant photosynthetic organs–Testing for deciduous and dicotyledons. Ecol Indic. 2021; 121 :107210. doi: 10.1016/j.ecolind.2020.107210. [ CrossRef ] [ Google Scholar ]
• Ding Z, Wang Q, Hu X. Fractionation of Zn and Pb in bulk soil and size fractions of water-stable micro-aggregates of lead/zinc tailing soil under simulated acid rain. Procedia Environ Sci Eng Manag. 2011; 10 :325–330. doi: 10.1016/j.proenv.2011.09.053. [ CrossRef ] [ Google Scholar ]
• Dolatabadian A, Sanavy SAMM, Gholamhoseini M, Joghan AK, Majdi M, Kashkooli AB. The role of calcium in improving photosynthesis and related physiological and biochemical attributes of spring wheat subjected to simulated acid rain. Physiol Mol Biol Plants. 2013; 19 :189–198. doi: 10.1007/s12298-013-0165-7. [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Dörter M, Mağat-Türk E, Döğeroğlu T, Özden-Üzmez Ö, Gaga EO, Karakaş D, Yenisoy-Karakaş S (2022) An assessment of spatial distribution and atmospheric concentrations of ozone, nitrogen dioxide, sulfur dioxide, benzene, toluene, ethylbenzene, and xylenes: ozone formation potential and health risk estimation in Bolu city of Turkey. Environ Sci Pollut Res 1-15.10.1007/s11356-022-19608-x [ PubMed ]
• Driscoll CT, Wang Z (2019) Ecosystem effects of acidic deposition. In Encyclopedia of Water; American Cancer Society: New York, NY, USA, 1–12. 10.1002/9781119300762.wsts0043
• Du E, Dong D, Zeng X, Sun Z, Jiang X, de Vries W. Direct effect of acid rain on leaf chlorophyll content of terrestrial plants in China. Sci Total Environ. 2017; 605 :764–769. doi: 10.1016/j.scitotenv.2017.06.044. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Duncan BN, Lamsal LN, Thompson AM, Yoshida Y, Lu Z, Streets DG, Pickering KE. A space-based, high-resolution view of notable changes in urban NOx pollution around the world (2005–2014) J Geophys Res Atmos. 2016; 121 :976–996. doi: 10.1002/2015JD024121. [ CrossRef ] [ Google Scholar ]
• Dursun A, Yildirim E, Güvenc I, Kumlay AM (2000) Effects of simulated acid rain on plant growth and yield of tomato ( Lycopersicon esculentum ). In II Balk Symp Vegetables Potatoes 579:245–248.10.17660/ActaHortic.2002.579.40
• EEA (2013) European Union emission inventory report 1990–2011 under the UNECE Convention on Long-range Transboundary Air Pollution (LRTAP), European Environment Agency (EEA), Technical report No 10/2013. 10.2800/44480
• Eguagie MO, Aiwansoba RP, Omofomwan KO, Oyanoghafo OO. Impact of simulated acid rain on the growth, yield and plant component of Abelmoschus caillei . J Adv Biol Biotechnol. 2016; 6 :1–6. doi: 10.9734/JABB/2016/24804. [ CrossRef ] [ Google Scholar ]
• Evans LS (1988) Effect of acidic decomposition on vegetation: State of science. In: Rao D.N., M. Yunus, K.J. Ahmad, S.N. Singh, (eds) Perspectives in environmental botany, today and tomorrows. Printers and Publishers, New Delhi, pp 73–119
• Evans LS, Curry TM, Lewin KF. Responses of leaves of Phaseolus vulgaris L. to simulated acidic rain. New Phytol. 1981; 88 :403–420. doi: 10.1111/j.1469-8137.1981.tb04089.x. [ CrossRef ] [ Google Scholar ]
• Evans LS, Gmur NF, Mancini D. Effects of simulated acidic rain on yields of Raphanus sativus, Lactuca sativa, Triticum aestivum and Medicago sativa . Environ Exp Bot. 1982; 22 :445–453. doi: 10.1016/0098-8472(82)90055-7. [ CrossRef ] [ Google Scholar ]
• Evans LS, Lewin KF. Growth, development and yield responses of pinto beans and soybeans to hydrogen ion concentrations of simulated acidic rain. Environ Exp Bot. 1981; 21 :103–113. doi: 10.1016/0098-8472(81)90015-0. [ CrossRef ] [ Google Scholar ]
• Evans LS, Lewin KF, Conway CA, Patti MJ. Seed yields (quantity and quality) of field-grown soybeans exposed to simulated acidic rain. New Phytol. 1981; 89 :459–470. doi: 10.1111/j.1469-8137.1981.tb02327.x. [ CrossRef ] [ Google Scholar ]
• Fang HJ, Yu GR, Cheng SL, Mo JM, Yan JH, Li S. 13 C abundance, water-soluble and microbial biomass carbon as potential indicators of soil organic carbon dynamics in subtropical forests at different successional stages and subject to different nitrogen loads. Plant Soil. 2009; 320 :243–254. doi: 10.1007/s11104-009-9890-7. [ CrossRef ] [ Google Scholar ]
• Fei J, Ma J, Yang J, Liang Y, Ke Y, Yao L, Min X. Effect of simulated acid rain on stability of arsenic calcium residue in residue field. Environ Geochem Health. 2020; 42 :769–780. doi: 10.1007/s10653-019-00273-y. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Foell W (1995) RAINS-Asia: an assessment model for air pollution in Asia. Report on the World Bank Sponsored Project" Acid Rain and Emission Reduction in Asia"
• Francis AJ. Effects of acidic precipitation and acidity on soil microbial processes. Water Air Soil Poll. 1982; 18 :375–394. doi: 10.1007/BF02419425. [ CrossRef ] [ Google Scholar ]
• Frey SD, Ollinger S, Nadelhoffer KE, Bowden R, Brzostek E, Burton A, Wickings K. Chronic nitrogen additions suppress decomposition and sequester soil carbon in temperate forests. Biogeochemistry. 2014; 121 :305–316. doi: 10.1007/s10533-014-0004-0. [ CrossRef ] [ Google Scholar ]
• Gao YF, Rong LP, Zhao DH, Zhang JQ, Chen JS. Effects of simulated acid rain on the photosynthetic physiology of Acer ginnala seedlings. Can J for Res. 2021; 51 :18–24. doi: 10.1139/cjfr-2020-0091. [ CrossRef ] [ Google Scholar ]
• Garaga R, Chakraborty S, Zhang H, Gokhale S, Xue Q, Kota SH. Influence of anthropogenic emissions on wet deposition of pollutants and rainwater acidity in Guwahati, a UNESCO heritage city in Northeast India. Atmos Res. 2020; 232 :104683. doi: 10.1016/j.atmosres.2019.104683. [ CrossRef ] [ Google Scholar ]
• Gholami F, Tomas M, Gholami Z, Vakili M. Technologies for the nitrogen oxides reduction from flue gas: A review. Sci Total Environ. 2020; 714 :136712. doi: 10.1016/j.scitotenv.2020.136712. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Gilani MM, Tigabu M, Liu B, Farooq TH, Rashid MHU, Ramzan M, Ma X. Seed germination and seedling emergence of four tree species of southern China in response to acid rain. J for Res. 2021; 32 :471–481. doi: 10.1007/s11676-020-01102-0. [ CrossRef ] [ Google Scholar ]
• Gioda A, Reyes‐Rodríguez GJ, Santos‐Figueroa G, Collett Jr JL, Decesari S, Ramos MDCK, Bezerra Netto HJ, de Aquino Neto FR, Mayol‐Bracero OL (2011) Speciation of water‐soluble inorganic, organic, and total nitrogen in a background marine environment: Cloud water, rainwater, and aerosol particles. J Geophys Res Atmos. 10.1029/2010JD015010
• Global energy and CO 2 status report (2019). https://www.iea.org/reports/global-energy-co2-status-report-2019
• Gonçalves C, Santos MAD, Fornaro A, Pedrott JJ. Hydrogen peroxide in the rainwater of Sao Paulo megacity: measurements and controlling factors. J Braz Chem Soc. 2010; 21 :331–339. doi: 10.1590/S0103-50532010000200020. [ CrossRef ] [ Google Scholar ]
• Guo Y, Zhang J, Wang S, She F, Li J (2011) Chemical characteristics of atmospheric precipitation in spring and summer in Toyama, Japan. In 2011 Int Conf Remote Sens Environ Transp Eng 3917–3920. IEEE.10.1109/RSETE.2011.5965175
• Haruna MY, Khan AA, Darma ZU (2016) Effect of acid rain on growth of Papaya ( Carica papaya ) and Castor (Ricinus communis ) plants. J Sci Technol 9:43–47. 10.18780/e-jst.v9i1.738
• Heck WW, Heagle AS, Shriner DS. Hordeum vulgare exposed to long term fumigation with low concentration of SO 2 . Physiol Plant. 1986; 76 :445–450. [ Google Scholar ]
• Hernandez L, Probst A, Probst JL, Ulrich E. Heavy metal distribution in some French forest soils: evidence for atmospheric contamination. Sci Total Environ. 2003; 312 :195–219. doi: 10.1016/S0048-9697(03)00223-7. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Hosono T, Nouchi I. Effects of simulated acid rain on the growth of agricultural crops. J Agric Meteorol. 1993; 48 :743–746. doi: 10.2480/agrmet.48.743. [ CrossRef ] [ Google Scholar ]
• Hu H, Hua W, Shen A, Zhou H, Sheng L, Lou W, Zhang G. Photosynthetic rate and chlorophyll fluorescence of barley exposed to simulated acid rain. Environ Sci Pollut Res. 2021; 28 :42776–42786. doi: 10.1007/s11356-021-13807-8. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Hu XF, Chen FS, Wine ML, Fang XM. Increasing acidity of rain in subtropical tea plantation alters aluminum and nutrient distributions at the root-soil interface and in plant tissues. Plant Soil. 2017; 417 :261–274. doi: 10.1007/s11104-017-3256-3. [ CrossRef ] [ Google Scholar ]
• Hu XF, Wu AQ, Wang FC, Chen FS. The effects of simulated acid rain on internal nutrient cycling and the ratios of Mg, Al, Ca, N, and P in tea plants of a subtropical plantation. Environ Monit Assess. 2019; 191 :1–14. doi: 10.1007/s10661-019-7248-z. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Irie H, Muto T, Itahashi S, Kurokawa JI, Uno I. Turnaround of tropospheric nitrogen dioxide pollution trends in China, Japan, and South Korea. Sola. 2016; 12 :170–174. doi: 10.2151/sola.2016-035. [ CrossRef ] [ Google Scholar ]
• Ismail OM, Zohair MM. Date palm pollen germination and growth susceptibility to different pH medium. J Agr Food Technol. 2013; 3 :26–30. [ Google Scholar ]
• Itahashi S, Kurokawa J, Ohara T, Uno I, Fujita SI. The 36-Year Historical Variation of Precipitation Chemistry during 1976–2011 at Ryori WMO-GAW Station in Japan. SOLA. 2021 doi: 10.2151/sola.2021-032. [ CrossRef ] [ Google Scholar ]
• Ito A, Wakamatsu S, Morikawa T, Kobayashi S (2021) 30 years of air quality trends in Japan. Atmosphere 12(8):1072. 10.3390/atmos12081072
• Jang E, Do W, Park G, Kim M, Yoo E. Spatial and temporal variation of urban air pollutants and their concentrations in relation to meteorological conditions at four sites in Busan, South Korea. Atmos Pollut Res. 2017; 8 :89–100. doi: 10.1016/j.apr.2016.07.009. [ CrossRef ] [ Google Scholar ]
• Janta R, Sekiguchi K, Yamaguchi R, Sopajaree K, Plubin B, Chetiyanukornkul T (2020) Spatial and temporal variations of atmospheric PM10 and air pollutants concentration in upper Northern Thailand during 2006–2016. Appl Sci Eng Prog 13:256–267. 10.14416/j.asep.2020.03.007
• Jiao R, Zhang M, Wei Z, Xu J, Zhang H. Alleviative effects of nitric oxide on Vigna radiata seedlings under acidic rain stress. Mol Biol Rep. 2021; 48 :2243–2251. doi: 10.1007/s11033-021-06244-w. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Keresztesi Á, Birsan MV, Nita IA, Bodor Z, Szép R. Assessing the neutralisation, wet deposition and source contributions of the precipitation chemistry over Europe during 2000–2017. Environ Sci Eur. 2019; 31 :1–15. doi: 10.1186/s12302-019-0234-9. [ CrossRef ] [ Google Scholar ]
• Keresztesi Á, Nita IA, Boga R, Birsan MV, Bodor Z, Szép R. Spatial and long-term analysis of rainwater chemistry over the conterminous United States. Environ Res. 2020; 188 :109872. doi: 10.1016/j.envres.2020.109872. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Khare P, Satsangi GS, Kumar N, Kumari KM, Srivastava SS. HCHO, HCOOH and CH 3 COOH in air and rain water at a rural tropical site in north central India. Atmos Environ. 1997; 31 :3867–3875. doi: 10.1016/S1352-2310(97)00263-X. [ CrossRef ] [ Google Scholar ]
• Khemani LT, Momin GA, Rao PSP, Pillai AG, Safai PD, Mohan K, Rao MG. Atmospheric pollutants and their influence on acidification of rain water at an industrial location on the west coast of India. Atmos Environ. 1994; 28 :3145–3154. doi: 10.1016/1352-2310(94)00148-E. [ CrossRef ] [ Google Scholar ]
• Killham K, Firestone MK, Mc Coll JG. Acid rain and soil microbial activity: effects and their mechanisms. J Environ Qual. 1983; 12 :133–137. doi: 10.2134/jeq1983.00472425001200010024x. [ CrossRef ] [ Google Scholar ]
• Kim AY, Kim JY, Ko MS, Kim KW. Acid rain impact on phytoavailability of heavy metals in soils. Geosystem Eng. 2010; 13 :133–138. doi: 10.1080/12269328.2010.10541320. [ CrossRef ] [ Google Scholar ]
• Knittel R, Pell EJ. Effects of drought stress and simulated acidic rain on foliar conductance of Zea mays L. Environ Exp Bot. 1991; 31 :79–90. doi: 10.1016/0098-8472(91)90010-L. [ CrossRef ] [ Google Scholar ]
• Kowalok ME. Common threads: Research lessons from acid rain, ozone depletion, and global warming. Environ Sci Policy Sustain Dev. 1993; 35 :12–38. doi: 10.1080/00139157.1993.9929107. [ CrossRef ] [ Google Scholar ]
• Krotkov NA, McLinden CA, Li C, Lamsal LN, Celarier EA, Marchenko SV, Swartz WH, Bucsela EJ, Joiner J, Duncan BN, Boersma KF (2016) Aura OMI observations of regional SO 2 and NO 2 pollution changes from 2005 to 2015.Atmos Chem Phys 16:605-4629. 10.5194/a5-2016
• Kumar P, Yadav S, Kumar A. Sources and processes governing rainwater chemistry in New Delhi, India. Nat Hazards. 2014; 74 :2147–2162. doi: 10.1007/s11069-014-1295-0. [ CrossRef ] [ Google Scholar ]
• Kuttippurath J, Patel VK, Pathak M, Singh A (2022) Improvements in SO 2 pollution in India: role of technology and environmental regulations. Environ Sci Pollut Res 1–13. 10.1007/s11356-022-21319-2 [ PMC free article ] [ PubMed ]
• Le Bolloch O, Guerzoni S. Acid and alkaline deposition in precipitation on the Western coast of Sardinia, Central Mediterranean (40 N, 8 E) Wat Air Soil Poll. 1995; 85 :2155–2160. doi: 10.1007/BF01186153. [ CrossRef ] [ Google Scholar ]
• Lee JJ, Neely GE, Perrigan SC, Grothaus LC. Effect of simulated sulfuric acid rain on yield, growth and foliar injury of several crops. Environ Exp Bot. 1981; 21 :171–185. doi: 10.1016/0098-8472(81)90024-1. [ CrossRef ] [ Google Scholar ]
• Lee JJ, Weber DE. The effect of simulated acid rain on seedling emergence and growth of eleven woody species. For Sci. 1979; 25 :393–398. doi: 10.1093/forestscience/25.3.393. [ CrossRef ] [ Google Scholar ]
• Legrand M, Preunkert S, Galy‐Lacaux C, Liousse C, Wagenbach D (2005) Atmospheric year‐round records of dicarboxylic acids and sulfate at three French sites located between 630 and 4360 m elevation. J Geophys Res Atmos 110:D13302. 10.1029/2004JD005515
• Li C, McLinden C, Fioletov V, Krotkov N, Carn S, Joiner J, Streets D, He H, Ren X, Li Z, Dickerson RR (2017). India is overtaking China as the world’s largest emitter of anthropogenic sulfur dioxide. Sci Rep 7:1-7. 10.1038/s41598-017-14639-8 [ PMC free article ] [ PubMed ]
• Li HR, Xiang HM, Zhong JW, Ren XQ, Wei H, Zhang JE, Zhao BL. Acid Rain Increases Impact of Rice Blast on Crop Health via Inhibition of Resistance Enzymes. Plants. 2020; 9 :881. doi: 10.3390/plants9070881. [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Li J, Jia C, Lu Y, Tang S, Shim H. Multivariate analysis of heavy metal leaching from urban soils following simulated acid rain. Microchem J. 2015; 122 :89–95. doi: 10.1016/j.microc.2015.04.015. [ CrossRef ] [ Google Scholar ]
• Li J, Wu H, Jiang P, Fu C. Rainwater chemistry in a subtropical high-altitude mountain site, South China: Seasonality, source apportionment and potential factors. Atmos Environ. 2022; 268 :118786. doi: 10.1016/j.atmosenv.2021.118786. [ CrossRef ] [ Google Scholar ]
• Li X, Wang Y, Zhang Y, Wang Y, Pei C. Response of soil chemical properties and enzyme activity of four species in the Three Gorges Reservoir area to simulated acid rain. Ecotoxicol Environ Saf. 2021; 208 :111457. doi: 10.1016/j.ecoenv.2020.111457. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Liang Chanjuan, Ge Yuqing, Su Lei, Bu Jinjin. Response of plasma membrane H+-ATPase in rice (Oryza sativa) seedlings to simulated acid rain. Environmental Science and Pollution Research. 2015; 22 (1):535–545. doi: 10.1007/s11356-014-3389-3. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Ling DJ, Huang QC, Ouyang Y. Impacts of simulated acid rain on soil enzyme activities in a latosol. Ecotoxicol Environ Saf. 2010; 73 :1914–1918. doi: 10.1016/j.ecoenv.2010.07.024. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Liu H, Ren X, Zhu J, Wu X, Liang C. Effect of exogenous abscisic acid on morphology, growth and nutrient uptake of rice ( Oryza sativa ) roots under simulated acid rain stress. Planta. 2018; 248 :647–659. doi: 10.1007/s00425-018-2922-x. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Liu TW, Niu L, Fu B, Chen J, Wu FH, Chen J, Zheng HL. A transcriptomic study reveals differentially expressed genes and pathways respond to simulated acid rain in Arabidopsis thaliana . Genome. 2013; 56 :49–60. doi: 10.1139/gen-2012-0090. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Liu X, Fu Z, Zhang B, Zhai L, Meng M, Lin J, Zhang J. Effects of sulfuric, nitric, and mixed acid rain on Chinese fir sapling growth in Southern China. Ecotoxicol Environ Saf. 2018; 160 :154–161. doi: 10.1016/j.ecoenv.2018.04.071. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Liu X, Li C, Meng M, Zhai L, Zhang B, Jia Z, Zhang J. Comparative effects of the recovery from sulfuric and nitric acid rain on the soil enzyme activities and metabolic functions of soil microbial communities. Sci Total Environ. 2020; 714 :136788. doi: 10.1016/j.scitotenv.2020.136788. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Liu X, Meng M, Zhang Y, Li C, Ma S, Li Q, Zhang J. Effects of sulfuric, nitric, and mixed acid rain on the decomposition of fine root litter in Southern China. Ecol Process. 2021; 10 :1–13. doi: 10.1186/s13717-021-00334-0. [ CrossRef ] [ Google Scholar ]
• Liu X, Zhang B, Zhao W, Wang L, Xie D, Huo W, Zhang J. Comparative effects of sulfuric and nitric acid rain on litter decomposition and soil microbial community in subtropical plantation of Yangtze River Delta region. Sci Total Environ. 2017; 601 :669–678. doi: 10.1016/j.scitotenv.2017.05.151. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Liu XD, Feng YJ, Mo QF, Chu GW, Li YL, Zhang QM, Zhou Q. Long-term changes of water acidity in an intact forested watershed in south China. J Mt Sci. 2021; 18 (12):3138–3146. doi: 10.1007/s11629-021-6929-6. [ CrossRef ] [ Google Scholar ]
• Liu Z, Yang J, Zhang J, Xiang H, Wei H. A bibliometric analysis of research on acid rain. Sustainability. 2019; 11 :3077. doi: 10.3390/su11113077. [ CrossRef ] [ Google Scholar ]
• Lv Y, Wang C, Jia Y, Wang W, Ma X, Du J, Tian X. Effects of sulfuric, nitric, and mixed acid rain on litter decomposition, soil microbial biomass, and enzyme activities in subtropical forests of China. Appl Soil Ecol. 2014; 79 :1–9. doi: 10.1016/j.apsoil.2013.12.002. [ CrossRef ] [ Google Scholar ]
• Ma J, Zhong B, Khan MA, Wu D, Zhu Y, Wang Y, Xie X, Liu H, Liu D (2021) Transport of mobile particles in heavy metal contaminated soil with simulated acid rain leaching. Bull Environ Contam Toxicol 106:965-969. 10.1007/s00128-021-03269-6 [ PubMed ]
• Ma S, Chen W, Zhang J, Shen H (2020) Influence of simulated acid rain on the physiological response of flowering Chinese cabbage and variation of soil nutrients. Plant Soil Environ 66:648–657.10.17221/469/2020-PSE
• Ma Y, Wang B, Zhang R, Gao Y, Zhang X, Li Y, Zuo Z. Initial simulated acid rain impacts reactive oxygen species metabolism and photosynthetic abilities in Cinnamonum camphora undergoing high temperature. Ind Crops Prod. 2019; 135 :352–361. doi: 10.1016/j.indcrop.2019.04.050. [ CrossRef ] [ Google Scholar ]
• Majd A, Chehregani AH (1992) Studies on developmental processes in ovules of soya Glycine max L. Plants and effects of certain toxins and environmental pollutants. In: Int Symp Transplant Prod Syst 319:431–436.10.17660/ActaHortic.1992.319.67
• Malaysia SA (1983) The state of the Malaysian environment 1983–1984. SAM, Penang, Malaysia (Original not seen: cited from McCormick, J. 1985. Acid earth. Earthscan Pub, International Institute for Environment and Development, London, UK.)
• Mallick S, Kumar A, Kumar P. Oxidation of HOSO[rad] by NH 2 [rad]: A new path for the formation of an acid rain precursor. Chem Phys Lett. 2021; 773 :138536. doi: 10.1016/j.cplett.2021.138536. [ CrossRef ] [ Google Scholar ]
• Maltz MR, Chen Z, Cao J, Arogyaswamy K, Shulman H, Aronson EL. Inoculation with Pisolithus tinctorius may ameliorate acid rain impacts on soil microbial communities associated with Pinus massoniana seedlings. Fungal Ecol. 2019; 40 :50–61. doi: 10.1016/j.funeco.2018.11.011. [ CrossRef ] [ Google Scholar ]
• Mannings S, Smith S, Bell JNB. Effect of acid deposition on soil acidification and metal mobilisation. Appl Geochemistry. 1996; 11 :139–143. doi: 10.1016/0883-2927(95)00077-1. [ CrossRef ] [ Google Scholar ]
• Meenakshi S, Sharma VP. Effect of acid rain on the contents of leaves of Solanum melongena . J Plant Dev Sci. 2011; 3 :169–173. [ Google Scholar ]
• Merino A, Fernandez V, Garcia-Rodeja E (1994) Effects of experimental acidification of acid soils from Galicia (NW Spain). II. Heavy metal mobilization, 3rd Int Symp Environ Geochem Kraków, Book of Abstracts, 280–281.
• Milton MB, Abigael TO. Effects of simulated acid rain on the morphology, phenology and yield of Okra ( Abelmoschus esculentus (L). Moench) J Environ Sci Comp Sci Engg Technol. 2015; 4 :501–518. [ Google Scholar ]
• Mishima SI, Kimura SD, Eguchi S, Shirato Y. Changes in soil available-nutrient stores and relationships with nutrient balance and crop productivity in Japan. Soil Sci Plant Nutr. 2013; 59 :371–379. doi: 10.1080/00380768.2013.786646. [ CrossRef ] [ Google Scholar ]
• Mo J, Zhang W, Zhu W, Gundersn P, Fang Y, Li D, Wang H. Nitrogen addition reduces soil respiration in a mature tropical forest in southern China. Glob Chang Biol. 2008; 14 :403–412. doi: 10.1111/j.1365-2486.2007.01503.x. [ CrossRef ] [ Google Scholar ]
• Mohajan H (2018) Acid rain is a local environment pollution but global concern. 47–55
• Moreda-Piñeiro J, Alonso-Rodríguez E, Moscoso-Pérez C, Blanco-Heras G, Turnes-Carou I, López-Mahía P, Prada-Rodríguez D. Influence of marine, terrestrial and anthropogenic sources on ionic and metallic composition of rainwater at a suburban site (northwest coast of Spain) Atmos Environ. 2014; 88 :30–38. doi: 10.1016/j.atmosenv.2014.01.067. [ CrossRef ] [ Google Scholar ]
• Munzuroglu O, Obek E, Geckil H. Effects of simulated acid rain on the pollen germination and pollen tube growth of apple ( Malus sylvestris miller cv. golden) Acta Biol Hung. 2003; 54 :95–103. doi: 10.1556/ABiol.54.2003.1.10. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Nandlal Hemlata Singh, Sachan Priti (2017) Simulated Acid Rain-induced Alterations in Flowering, Leaf Abscission and Pollen Germination in Sunflower ( Helianthus annuus L.). Journal of Applied Sciences and Environmental Management 21(2):290. 10.4314/jasem.v21i2.9
• National Automobile Scrappage Policy (2021) Ministry of road transport and highways website. https://morth.nic.in/vehiclescrapping-policy-overview
• Neufeld HS, Jernstedt JA, Haines BL. Direct foliar effects of simulated acid rain: I. Damage, growth and gas exchange. New Phytol. 1985; 99 :389–405. doi: 10.1111/j.1469-8137.1985.tb03667.x. [ CrossRef ] [ Google Scholar ]
• Neves NR, Oliva MA, da Cruz CD, Costa AC, Ribas RF, Pereira EG. Photosynthesis and oxidative stress in the restinga plant species Eugenia uniflora L. exposed to simulated acid rain and iron ore dust deposition: potential use in environmental risk assessment. Sci Total Environ. 2009; 407 :3740–3745. doi: 10.1016/j.scitotenv.2009.02.035. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Odiyi BO, Bamidele JF. Effects of simulated acid rain on growth and yield of Cassava Manihot esculenta (Crantz) J Agric Sci. 2014; 6 :96. doi: 10.5539/jas.v6n1p96. [ CrossRef ] [ Google Scholar ]
• Odiyi BO, Eniola AO. The effect of simulated acid rain on plant growth component of cowpea ( Vigna unguiculata ) L. Walps Jordan J Biol Sci. 2015; 8 :51–54. doi: 10.12816/0026948. [ CrossRef ] [ Google Scholar ]
• Paulot F, Wunch D, Crounse JD, Toon GC, Millet DB, DeCarlo PF, Wennberg PO. Importance of secondary sources in the atmospheric budgets of formic and acetic acids. Atmos Chem Phys. 2011; 11 :1989–2013. doi: 10.5194/acpd-10-24435-2010. [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Peña RM, García S, Herrero C, Losada M, Vázquez A, Lucas T. Organic acids and aldehydes in rainwater in a northwest region of Spain. Atmos Environ. 2002; 36 :5277–5288. doi: 10.1016/S1352-2310(02)00648-9. [ CrossRef ] [ Google Scholar ]
• Pham Ha T. T., Nguyen An Thinh, Do Anh T. Ngoc., Hens Luc. Impacts of Simulated Acid Rain on the Growth and the Yield of Soybean (Glycine max (L.) Merr.) in the Mountains of Northern Vietnam. Sustainability. 2021; 13 (9):4980. doi: 10.3390/su13094980. [ CrossRef ] [ Google Scholar ]
• Polishchuk OV, Vodka MV, Belyavskaya NA, Khomochkin AP, Zolotareva EK. The effect of acid rain on ultrastructure and functional parameters of photosynthetic apparatus in pea leaves. Cell Tissue Biol. 2016; 10 :250–257. doi: 10.1134/S1990519X16030093. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Popova T, Petrova T, Petrichev M, Valyova M. Action of activated waters on plants after adverse chemical effects, imitating acid rain. Bulg J Agric Sci. 2019; 25 :638–645. [ Google Scholar ]
• Prathibha P, Kothai P, Saradhi IV, Pandit GG, Puranik VD. Chemical characterization of precipitation at a coastal site in Trombay, Mumbai, India. Environ Monit Assess. 2010; 168 :45–53. doi: 10.1007/s10661-009-1090-7. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Rahman MM, Mahamud S, Thurston GD. Recent spatial gradients and time trends in Dhaka, Bangladesh, air pollution and their human health implications. J Air Waste Manag Assoc. 2019; 69 :478–501. doi: 10.1080/10962247.2018.1548388. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Raju R, Paul AG, Aguilor UP, Capili JT (2021) The Effect of Induced Acid Rain; Allium cepa Chromosomal Aberration Assay. Sch Acad J Biosci 9:89–97. 10.36347/sajb.2021.v09i03.005
• Ramlall C, Varghese B, Ramdhani S, Pammenter NW, Bhatt A, Berjak P. Effects of simulated acid rain on germination, seedling growth and oxidative metabolism of recalcitrant-seeded Trichilia dregeana grown in its natural seed bank. Physiol Plant. 2015; 153 :149–160. doi: 10.1111/ppl.12230. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Renzoni, GC, Viegi, L (1991) In vitro sensitivity of Pinus pinaster and P. pinea pollen grains to different pH values. Ann Bot Fenn 28(2):135–142
• Rao PSP, Tiwari S, Matwale JL, Pervez S, Tunved P, Safai PD, Hopke PK. Sources of chemical species in rainwater during monsoon and non-monsoonal periods over two mega cities in India and dominant source region of secondary aerosols. Atmos Environ. 2016; 146 :90–99. doi: 10.1016/j.atmosenv.2016.06.069. [ CrossRef ] [ Google Scholar ]
• Rodríguez-Sánchez VM, Rosas U, Calva-Vásquez G, Sandoval-Zapotitla E. Does acid rain alter the leaf anatomy and photosynthetic pigments in urban trees? Plants. 2020; 9 :862. doi: 10.3390/plants9070862. [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Roy A, Chatterjee A, Tiwari S, Sarkar C, Das SK, Ghosh SK, Raha S. Precipitation chemistry over urban, rural and high altitude Himalayan stations in eastern India. Atmos Res. 2016; 181 :44–53. doi: 10.1016/j.atmosres.2016.06.005. [ CrossRef ] [ Google Scholar ]
• Sen TK, Khilar KC. Review on subsurface colloids and colloid-associated contaminant transport in saturated porous media. Adv Colloid Interface Sci. 2006; 119 :71–96. doi: 10.1016/j.cis.2005.09.001. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Shah J, Nagpal T, Johnson T, Amann M, Carmichael G, Foell W, Streets D. Integrated analysis for acid rain in Asia: policy implications and results of RAINS-ASIA model. Annu Rev Environ Resour. 2000; 25 :339–375. doi: 10.1146/annurev.energy.25.1.339. [ CrossRef ] [ Google Scholar ]
• Shah V, Jacob D, Moch JM, Wang X, Zhai S (2020). Global modeling of cloudwater acidity, rainwater acidity, and acid inputs to ecosystems. In AGU Fall Meeting Abstracts A74–13.
• Shivashankara GP, Ranga K, Ramalingaiah M. Characterisation of bulk precipitation in industrial areas of Bangalore city. Indian J Environ Health. 1999; 41 :229–238. [ Google Scholar ]
• Shripal N, Pal KS, Kumar N. Effects of simulated acid rain on yield and carbohydrate contents of green pepper. Advan Plant Sci. 2000; 13 :85–88. [ Google Scholar ]
• Shu X, Zhang K, Zhang Q, Wang W (2019) Ecophysiological responses of Jatropha curcas L. seedlings to simulated acid rain under different soil types. Ecotoxicol Environ Saf 185:1-12. 10.1016/j.ecoenv.2019.109705 [ PubMed ]
• Singh A, Agrawal M. Response of two cultivars of Triticum aestivum L. to simulated acid rain. Environ Pollut. 1996; 91 :161–167. doi: 10.1016/0269-7491(95)00056-9. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Singh A, Agrawal M. Acid rain and its ecological consequences. J Environ Biol. 2007; 29 :15. [ PubMed ] [ Google Scholar ]
• Singh AK, Mondal GC, Kumar S, Singh KK, Kamal KP, Sinha A. Precipitation chemistry and occurrence of acid rain over Dhanbad, coal city of India. Environ Monit Assess. 2007; 125 :99–110. doi: 10.1007/s10661-006-9243-4. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Singh B, Agrawal M. Impact of simulated acid rain on growth and yield of two cultivars of wheat. Wat Air Soil Poll. 2004; 152 :71–80. doi: 10.1023/B:WATE.0000015331.02874.df. [ CrossRef ] [ Google Scholar ]
• Singh N, Yunus M, Singh SN, Ahmad KJ. Performance of Vicia faba plants in relation to simulated acid rain and/or endosulphan treatment. Bull Environ Contam Toxicol. 1992; 48 :243–248. doi: 10.1007/BF00194378. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Singh RK, Agrawal M. Atmospheric depositions around a heavily industrialized area in a seasonally dry tropical environment of India. Environ Pollut. 2005; 138 :142–152. doi: 10.1016/j.envpol.2005.02.009. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Sinsabaugh RL. Phenol oxidase, peroxidase and organic matter dynamics of soil. Soil Biol Biochem. 2010; 42 :391–404. doi: 10.1016/j.soilbio.2009.10.014. [ CrossRef ] [ Google Scholar ]
• Smith RA (1872) Air and rain: the beginnings of a chemical climatology. Longmans, Green, and Company, 600pp, London.
• Sridharan PV, Saksena S (1990) Description of acid rain problem in India. In: Second Annual Workshop on Acid Rain and Emissions in Asia. Bangkok, Thailand
• Sullivan TS, Barth VP, Lewis RW (2017) Soil acidity impacts beneficial soil microorganisms. Washington State University Extension and the U.S. Department of Agriculture 1-6.
• Sun X, Wang Y, Li H, Yang X, Sun L, Wang X, Wang W. Organic acids in cloud water and rainwater at a mountain site in acid rain areas of South China. Environ Sci Pollut Res. 2016; 23 :9529–9539. doi: 10.1007/s11356-016-6038-1. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Sutton MA, Drewer J, Moring A, Adhya TK, Ahmed A, Bhatia A, Brownlie W, Dragosits U, Ghude SD, Hillier J, Hooda S (2017) The Indian nitrogen challenge in a global perspective. The Indian Nitrogen Assessment. 10.1016/B978-0-12-811836-8.00002-1
• Swartz JS, Van Zyl PG, Beukes JP, Labuschagne C, Brunke EG, Portafaix T, Pienaar JJ. Twenty-one years of passive sampling monitoring of SO 2 , NO 2 and O 3 at the Cape Point GAW station. South Africa Atmos Environ. 2020; 222 :117128. doi: 10.1016/j.atmosenv.2019.117128. [ CrossRef ] [ Google Scholar ]
• Tang L, Lin Y, He X, Han G. Acid rain decelerates the decomposition of Cunninghamia lanceolata needle and Cinnamomum camphora leaf litters in a karst region in China. Ecol Res. 2019; 34 :193–200. doi: 10.1016/B978-0-12-811836-8.00002-1. [ CrossRef ] [ Google Scholar ]
• Tiwari S, Hopke PK, Thimmaiah D, Dumka UC, Srivastava AK, Bisht DS, Tripathi SN. Nature and sources of ionic species in precipitation across the Indo-Gangetic Plains, India. Aerosol Air Qual Res. 2016; 16 :943–957. doi: 10.4209/aaqr.2015.06.0423. [ CrossRef ] [ Google Scholar ]
• Tiwari S, Srivastava MK, Bisht DS (2008) Chemical composition of rainwater in Panipat, an industrial city in Haryana. Indian J Radio Space Phys 37:443–449.
• Tong S, Zhang L (2014) Differential sensitivity of growth and net photosynthetic rates in five tree species seedlings under simulated acid rain stress. Pol J Environ Stud 23(6): 2259-2264. 10.15244/pjoes/24930
• US EPA progress report (2013) 2012 Progress report, clean air markets. https://www3.epa.gov/airmarkets/progress/reports/ , https://www.epa.gov/sites/default/files/2015-08/documents/arpcair12_02.pdf
• Varma GS. Impact of soil-derived aerosols on precipitation acidity in India. Atmos Environ. 1989; 23 :2723–2728. doi: 10.1016/0004-6981(89)90552-0. [ CrossRef ] [ Google Scholar ]
• Varma GS. Background trends of pH of precipitation over India. Atmos Environ. 1989; 23 :747–751. doi: 10.1016/0004-6981(89)90476-9. [ CrossRef ] [ Google Scholar ]
• Waghmare VV, Aslam MY, Yang L, Safai PD, Pandithurai G (2021) Inorganic Ionic Composition of Rainwater at a High Altitude Station over the Western Ghats in Peninsular India. J Atmos Chem 78:59–76. 10.1007/s10874-021-09416-x
• Wang B, Wang C, Xue R, Liu M, Xu G, Li Z (2021). Earthworm and arbuscular mycorrhizal fungi improve plant hormones and antioxidant enzymes to alleviate simulated acid rain stress. 10.21203/rs.3.rs-438862/v1
• Wang Y, Xu Y, Li D, Tang B, Man S, Jia Y, Xu H. Vermicompost and biochar as bio-conditioners to immobilize heavy metal and improve soil fertility on cadmium contaminated soil under acid rain stress. Sci Total Environ. 2018; 621 :1057–1065. doi: 10.1016/j.scitotenv.2017.10.121. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Watanabe K, Honoki H. Measurements of aerosol number concentrations and rainwater chemistry at Mt. Tateyama, near the coast of the Japan sea in central Japan: On the influence of high-elevation Asian dust particles in autumn. J Atmos Chem. 2013; 70 :115–129. doi: 10.1007/s10874-013-9258-5. [ CrossRef ] [ Google Scholar ]
• Wei H, Liu Y, Xiang H, Zhang J, Li S, Yang J. Soil pH responses to simulated acid rain leaching in three agricultural soils. Sustainability. 2020; 12 :280. doi: 10.3390/su12010280. [ CrossRef ] [ Google Scholar ]
• Wei X, Blanco JA, Jiang H, Kimmins JH. Effects of nitrogen deposition on carbon sequestration in Chinese fir forest ecosystems. Sci Total Environ. 2012; 416 :351–361. doi: 10.1016/j.scitotenv.2011.11.087. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Wen K, Liang C, Wang L, Hu G, Zhou Q. Combined effects of lanthanum ion and acid rain on growth, photosynthesis and chloroplast ultrastructure in soybean seedlings. Chemosphere. 2011; 84 :601–608. doi: 10.1016/j.chemosphere.2011.03.054. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Wertheim FS, Craker LE. Effects of acid rain on corn silks and pollen germination. J Environ Qual. 1988; 17 :135–138. doi: 10.2134/jeq1989.00472425001800010023x. [ CrossRef ] [ Google Scholar ]
• World energy outlook 2019 assessed from https://www.iea.org/reports/world-energy-outlook-2019
• World Health Organization (WHO), world air quality report 2018. https://www.iqair.com/world-most-polluted . cities/world-air-quality-report-2018-en.pdf
• Wu J, Liang G, Hui D, Deng Q, Xiong X, Qiu Q, Zhang D. Prolonged acid rain facilitates soil organic carbon accumulation in a mature forest in Southern China. Sci Total Environ. 2016; 544 :94–102. doi: 10.1016/j.scitotenv.2015.11.025. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Xu Z, Wu Y, Liu WJ, Liang CS, Ji J, Zhao T, Zhang X. Chemical composition of rainwater and the acid neutralizing effect at Beijing and Chizhou city, China. Atmos Res. 2015; 164 :278–285. doi: 10.1016/j.atmosres.2015.05.009. [ CrossRef ] [ Google Scholar ]
• Yadav DS, Jaiswal B, Gautam M, Agrawal M (2020) Soil Acidification and its Impact on Plants. In: Plant Responses to Soil Pollution. Springer, Singapore, pp 1–26 10.1007/978-981-15-4964-9_1
• Yang L, Xu Y, Zhang R, Wang X, Yang C. Comprehensive transcriptome profiling of soybean leaves in response to simulated acid rain. Ecotoxicol Environ Saf. 2018; 158 :18–27. doi: 10.1016/j.ecoenv.2018.04.015. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Yin P, Peng YJ, Song CC, Liu XJ, Huang J, Lv X (2021). Effects of simulated acid rain on Growth of Lolium perenne . In: IOP Conf Ser: Earth Environ Sci. IOP Publishing, pp 022078. 10.1088/1755-1315/714/2/022078
• Zhang C, Yi X, Zhou F, Gao X, Wang M, Chen J, Shen C. Comprehensive transcriptome profiling of tea leaves ( Camellia sinensis ) in response to simulated acid rain. Sci Hortic. 2020; 272 :109491. doi: 10.1016/j.scienta.2020.109491. [ CrossRef ] [ Google Scholar ]
• Zhang JE, Ouyang Y, Ling DJ. Impacts of simulated acid rain on cation leaching from the Latosol in south China. Chemosphere. 2007; 67 :2131–2137. doi: 10.1016/j.chemosphere.2006.12.095. [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Zhao C, Sun Y, Zhong Y, Xu S, Liang Y, Liu S, He M. Spatio-temporal analysis of urban air pollutants throughout China during 2014–2019. Air Qual Atmos Health. 2021; 14 :1619–1632. doi: 10.1007/s11869-021-01043-5. [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Zheng W, Li R, Yang Q, Zhang W, Huang K, Guan X, Wang S. Short-term response of soil respiration to simulated acid rain in Cunninghamia lanceolata and Michelia acclurei plantations. J Soils Sediments. 2019; 19 :1239–1249. doi: 10.1007/s11368-018-2148-3. [ CrossRef ] [ Google Scholar ]
• Zhou S, Zhang M, Chen S, Xu W, Zhu L, Gong S, Wang P. Acid resistance of Masson pine ( Pinus massoniana Lamb.) families and their root morphology and physiological response to simulated acid deposition. Sci Rep. 2020; 10 :1–13. doi: 10.1038/s41598-020-79043-1. [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Zhou X, Xu Z, Liu W, Wu Y, Zhao T, Jiang H, Zhang X, Zhang J, Zhou L, Wang Y. Chemical composition of precipitation in Shenzhen, a coastal mega-city in South China: Influence of urbanization and anthropogenic activities on acidity and ionic composition. Sci Total Environ. 2019; 662 :218–226. doi: 10.1016/j.scitotenv.2019.01.096. [ PubMed ] [ CrossRef ] [ Google Scholar ]

Acid Rain and Our Ecosystem

More than 150 years after acid rain was first identified, scientists now see success in recovery from its damaging effects

Cassandra Willyard

Geologist Rich April climbs the small hill behind Colgate University and makes his way into the cemetery. He stops before a white marble pillar erected in 1852. The inscription is nearly illegible. Over time, any stone exposed to the elements will weather, April explains, but this marble has weathered unnaturally fast. The culprit? Acid rain.

April pulls a vial of acid from his pocket to demonstrate. He unscrews the cap and lets a few drops leak onto the stone, where they fizz and bubble. The rain that fell throughout the Northeast in the latter half of the 20th century wasn’t as acidic as the liquid in April’s vial, but the principle is the same. Acid eats marble. Given enough time, it can erase even words meant to last an eternity.

The effects of acid rain extend far beyond graveyards. Acid rain destroyed fish populations in lakes and streams, harmed fragile soils and damaged millions of acres of forest worldwide.

These far-reaching effects illustrate the profound impact air pollution can have on the land. But the story of acid rain is also a tale of how understanding air pollution can lead to solutions. Due to overwhelming scientific evidence linking power plant emissions to acid rain and acid rain to the death of lakes, new regulations have dramatically cut emissions and cleaned up the rain that falls on the United States.

The term ‘acid rain’ was coined in the mid-1800s, when Robert Angus Smith, a Scottish chemist working in London, noticed that rain tended to be more acidic in areas with more air pollution and that buildings crumble faster in areas where coal is burned. But it took another century for scientists to realize that acid rain was a widespread environmental problem. Scandinavian scientists began to document acidic damage to lakes and streams in the 1950s. In 1963, Gene Likens, then at Dartmouth, and colleagues began collecting and testing the pH of rainwater in New Hampshire’s White Mountains as part of an ecosystem study. They were surprised to find that it was quite acidic, but they didn’t have much basis for comparison; at that time, scientists weren’t regularly measuring the pH of rainwater.

Likens took a job at Cornell a few years later and set up instruments to collect rainwater in the Finger Lakes region and soon observed that the rain in New York was roughly as acidic as rain in New Hampshire. “That was the first clue that we had that this might be some kind of a regional phenomenon,” he says. But neither Likens nor his colleagues had a clear idea what the cause might be.

Likens won a fellowship that took him to Sweden in 1969, a serendipitous event, he says, because he met Svante Odén, a scientist at Uppsala University who had observed the same trends in Sweden that Likens had been observing in the Northeastern United States. Odén had his finger on a potential cause. “He was trying to build a case that [acid rain] might be due to emissions coming from the more industrialized areas of Europe,” Likens recalls.

Likens and his colleagues traced the emissions from coal-fired power plants and examined satellite and aircraft data, and they found a similar long-distance link. “Sure enough, the emissions were coming primarily from Midwestern states like Indiana, Ohio, Illinois and Kentucky,” Likens recalls. “They were making their way literally thousands of kilometers to New England and southeastern Canada and coming back down as acids.”

He reported his findings in Science in 1974, and the story was immediately picked up by newspapers. The phone didn’t stop ringing for months, Likens recalls. “It was that media exposure that really put acid rain on the map in North America.”

Acid rain occurs, Likens and Odén and other scientists realized, when sulfur dioxide and nitrogen oxide enter the atmosphere and react with water to form sulfuric and nitric acids. Natural sources of these gases exist—volcanoes, for instance, belch out sulfur dioxide—but the vast majority comes from the burning of fossil fuels, especially by coal-fired power plants. The tall smokestacks allow pollution to travel long distances. According to studies conducted by Likens and his colleagues, normal rainwater has a pH of 5.2. During the 1970s and 1980s, when acid rain was at its worst, scientists recorded pH levels as low as 2.1, roughly 1,000 times more acidic.

Acid rain affected many parts of the United States, but the Northeast suffered the most ecological damage. The Adirondack Mountains proved especially susceptible. Many soils contain calcium carbonate or other minerals that can neutralize acid rain before it seeps into lakes and streams. “Unfortunately the Adirondacks have almost none,” April says. As a result, lakes and streams quickly became acidic, killing fish and other aquatic animals.

In the late 1970s, researchers surveyed 217 lakes above 2,000 feet in the Adirondacks and found that 51 percent were highly acidic. The news was so grim that scientists began attempting to breed more acid-tolerant strains of trout. One New York State employee compared the area to Death Valley. A decade later, a larger study that included 849 lakes higher than 1,000 feet found that 55 percent were either completely devoid of life or on the brink of collapse.

As the scientific evidence linking acid rain to power plant emissions and ecological damage mounted, battles erupted among industry, scientists and environmentalists. “The 1980s is a period I call the ‘acid rain wars,’” Likens says. “There was huge rancorous nasty controversy.” Environmentalists from Greenpeace climbed power plant smokestacks and hung banners in protest; scientists testified before Congress about the link between emissions and acid rain, the severity of the effects, and whether proposed legislation would have an impact; and the power industry questioned the science and argued that regulations would drive electricity rates sky high.

Congress passed several amendments to the Clean Air Act in 1990 that cut emissions of sulfur dioxide through a cap-and-trade scheme. The goal was a 50 percent reduction in sulfur dioxide emissions from 1980 levels. That goal was achieved in 2008, two years before the deadline, which was set for 2010. Sulfur dioxide emissions fell from 17.3 million tons in 1980 to 7.6 million tons in 2008, less than the 8.95 million tons required by 2010.

The effect has been remarkable. Doug Burns, a scientist at the U.S. Geological Survey in Troy, New York, who directs the National Acid Precipitation Assessment Program, says the rain falling in the Northeast today is about half as acidic as it was in the early 1980s. Consequently, surface waters have become less acidic and fragile ecosystems are beginning to recover.

In many places, however, recovery has been painfully slow. Scientists now know that acid rain not only acidified lakes and streams, it also leached calcium from forest soils. That calcium depletion has had devastating effects on trees, especially sugar maples and red spruce. Acid rain leaches calcium from the needles of red spruce, making them more susceptible to cold. It also leaches calcium and magnesium from the soil, which can stress sugar maples. In addition, acid rain allows aluminum to accumulate in the soil. When trees take up aluminum, their roots can become brittle.

Some researchers have tried adding calcium back into the forests to speed recovery. April is currently involved in one such experiment in the Adirondacks. Over the past four and a half years, the calcium has penetrated only the top 15 centimeters of forest soil. “It takes a really long time for [the calcium] to get back down into the soil,” April says, so it won’t be a quick fix.

April would like to see sulfur dioxide and other emissions curtailed even further. “We still have acid rain coming in,” he says. “Some lakes look like they might be ready to come back, and if we cut the emissions more they would.”

Princeton University’s Michael Oppenheimer, who was a key player in the acid wars as chief scientist for the conservation group Environmental Defense Fund, agrees. “I think sulfur dioxide and nitrogen oxide need to be effectively eliminated,” he says. “We ought to head towards zero and see how close we can get.”

Although some effects of acid rain are lingering, most scientists consider it an environmental success story. “Science identified the problem. Science provided the guidelines for how to try to resolve the problem,” Likens says. “The success is that we have taken action as a society to try to deal with the problem.”

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Acid rain: Causes, effects and solutions

How acid rain affects nearly everything it touches, and what we can do about it.

Solutions and prevention

Additional resources, bibliography.

Acid rain, or acid deposition, is a broad term that includes any form of precipitation that contains acidic components, such as sulfuric acid or nitric acid. The precipitation is not necessarily wet or liquid; the definition includes dust, gases, rain, snow, fog and hail. The type of acid rain that contains water is called wet deposition. Acid rain formed with dust or gases is called dry deposition.

The precipitation is not necessarily wet or liquid; the definition includes dust, gasses, rain, snow, fog and hail. The type of acid rain that contains water is called wet deposition. Acid rain formed with dust or gasses is called dry deposition.

Causes of acid rain

The term acid rain was coined in 1852 by Scottish chemist Robert Angus Smith, according to the Royal Society of Chemistry, which calls him the "father of acid rain." Smith decided on the term while examining rainwater chemistry near industrial cities in England and Scotland. He wrote about his findings in 1872 in the book " Air and Rain: The Beginnings of a Chemical Climatology ." 

In the 1950s, scientists in the United States started studying the phenomenon, and in the 1960s and early 1970s, acid rain became recognized as a regional environmental issue that affected Western Europe and eastern North America.

Though manmade pollutants are currently affecting most acidic precipitation, natural disasters can be a factor as well. For example, volcanoes can cause acid rain by blasting pollutants into the air. These pollutants can be carried around the world in jet streams and turned into acid rain far from the volcano. After an asteroid supposedly wiped out the dinosaurs 65.5 million years ago, sulfur trioxide was blasted into the air. When it hit the air, it turned into sulfuric acid, generating a downpour of acid rain.

Even before that, over 4 billion years ago, it is suspected that the air may have had 10,000 times as much carbon dioxide as today. Geologists from the University of Wisconsin-Madison backed up this theory by studying rocks and publishing the results in a 2008 issue of the journal Earth and Planetary Science Letters. "At [those levels of carbon dioxide], you would have had vicious acid rain and intense greenhouse [effects]. That is a condition that will dissolve rocks," said study team member John Valley.

Sulfur dioxide (SO2) and nitrogen oxides (NOx) released into the air by fossil-fuel power plants, vehicles and oil refineries are the biggest cause of acid rain today, according to the Environmental Protection Agency (EPA). Two thirds of sulfur dioxide and one fourth of nitrogen oxide found in the atmosphere come from electric power generators. 

A chemical reaction happens when sulfur dioxide and nitrogen oxides mix with water, oxygen and other chemicals in the air. They then become sulfuric and nitric acids that mix with precipitation and fall to the ground. Precipitation is considered acidic when its pH level is about 5.2 or below. The normal pH of rain is around 5.6.

Environmental affects of acid rain

Acid rain affects nearly everything. Plants, soil, trees, buildings and even statues can be transformed by the precipitation.

Acid rain has been found to be very hard on trees. It weakens them by washing away the protective film on leaves, and it stunts growth. A United States Environmental Protection Agency ( EPA ) study showed that acid rain is particularly hard on trees.

"By providing the only preserved soil in the world collected before the acid rain era, the Russians helped our international team track tree growth for the first time with changes in soil from acid rain," said Greg Lawrence, a U.S. Geological Survey scientist. "We've known that acid rain acidifies surface waters, but this is the first time we've been able to compare and track tree growth in forests that include soil changes due to acid rain." 

Acid rain can also change the composition of soil and bodies of water, making them uninhabitable for local animals and plants. For example, healthy lakes have a pH of 6.5 or higher. As acid rain raises the level of acidity, fish tend to die off. Most fish species can't survive a water pH of below 5. When the pH becomes a 4, the lake is considered dead, according to National Atmospheric Deposition Program .

It can additionally deteriorate limestone and marble buildings and monuments, like gravestones. 

There are several solutions to stopping human-caused acid rain. Regulating the emissions coming from vehicles and buildings is an important step, according to the EPA. This can be done by restricting the use of fossil fuels and focusing on more renewable energy sources such as solar and wind power.

Related: How do solar panels work?

Also, each person can do their part by reducing their vehicle use. Using public transportation, walking, riding a bike or carpooling is a good start, according to the EPA. People can also reduce their use of electricity, which is widely created with fossil fuels , or switch to a solar plan. Many electricity companies offer solar packages to their customers that require no installation and low costs. 

It is also possible to prevent acid rain forming, by adding lime deposits to major water sources. This method has been used to neutralize the Ph levels in the water, which reduced the acidity, for thousands of years, the LA Times reported . These so-called "liming" operations have also been used to restore wildlife. In Wales, a liming operation was conducted in 2003 to restore salmon to the Wye river. The water had become too acidic for the fish to survive, causing them to disappear from the river 18 years earlier, Young People's Trust for the Environment , a U.K. non-profit organization, reported.

Discover key facts about acid rain on Young Peoples Trust for the Environment , watch this National Geographic video about the role of fossil fuels and pollution in creating acid rain, and learn more about what the WWF is doing to reduce emissions.

• Peringe Grennfelt, Anna Engleryd, Martin Forsius, Øystein Hov, Henning Rodhe & Ellis Cowling: Acid rain and air pollution: 50 years of progress in environmental science and policy
• Douglas A.Burns, Julian Aherne, David A.Gay, Christopher M.B.Lehmann: Acid rain and its environmental effects: Recent scientific advances
• Lesley Evans Ogden: Acid Rain: Researchers Addressing Its Lingering Effects  

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Acid rain and its environmental effects: Recent scientific advances

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The term ‘acid rain’ refers to atmospheric deposition of acidic constituents that impact the earth as rain, snow, particulates, gases, and vapor. Acid rain was first recognized by Ducros (1845) and subsequently described by the English chemist Robert Angus Smith (Smith, 1852) whose pioneering studies linked the sources to industrial emissions and included early observations of deleterious environmental effects (Smith, 1872). Smith's work was largely forgotten until the mid-20th century when observations began to link air pollution to the deposition of atmospheric sulfate (SO 4 2− ) and other chemical constituents, first near the metal smelter at Sudbury, Ontario, Canada, and later at locations in Europe, North America, and Australia (Gorham, 1961). Our modern understanding of acid rain as an environmental problem caused largely by regional emissions of sulfur dioxide (SO 2 ) and nitrogen oxides (NO x ) stems from observations in the 1960s and early 1970s in Sweden by Svante Odén (Odén, 1976), and in North America by Gene Likens and colleagues (Likens and Bormann, 1974). These scientists and many who followed showed the link to emissions from coal-fired power plants and other industrial sources, and documented the environmental effects of acid rain such as the acidification of surface waters and toxic effects on vegetation, fish, and other biota.

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Acid rain and air pollution: 50 years of progress in environmental science and policy

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• Published: 21 September 2019
• Volume 49 , pages 849–864, ( 2020 )

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• Peringe Grennfelt   ORCID: orcid.org/0000-0002-0896-7924 1 ,
• Anna Engleryd 2 ,
• Martin Forsius 3 ,
• Øystein Hov 4 ,
• Henning Rodhe 5 &
• Ellis Cowling 6  

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Because of its serious large-scale effects on ecosystems and its transboundary nature, acid rain received for a few decades at the end of the last century wide scientific and public interest, leading to coordinated policy actions in Europe and North America. Through these actions, in particular those under the UNECE Convention on Long-range Transboundary Air Pollution, air emissions were substantially reduced, and ecosystem impacts decreased. Widespread scientific research, long-term monitoring, and integrated assessment modelling formed the basis for the policy agreements. In this paper, which is based on an international symposium organised to commemorate 50 years of successful integration of air pollution research and policy, we briefly describe the scientific findings that provided the foundation for the policy development. We also discuss important characteristics of the science–policy interactions, such as the critical loads concept and the large-scale ecosystem field studies. Finally, acid rain and air pollution are set in the context of future societal developments and needs, e.g. the UN’s Sustainable Development Goals. We also highlight the need to maintain and develop supporting scientific infrastructures.

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Introduction

Acid rain was one of the most important environmental issues during the last decades of the twentieth century. It became a game changer both scientifically and policy-wise. For some time, particularly during the 1980s, acid rain was by many considered to be one of the largest environmental threats of the time. Observations of fish extinction in Scandinavian surface waters and forest dieback on the European Continent were top stories in the news media. Even in North America acid rain received large public and policy attention.

During the cold war, with almost no contacts between East and West, acid rain broke the ice and formed an opening for scientific and political collaboration, resulting in a treaty under the United Nations’ Economic Commission for Europe (UNECE), the Convention on Long-range Transboundary Air Pollution (often mentioned as CLRTAP but in this paper we call it the Air Convention) signed in 1979. Eight protocols have been signed under the Air Convention committing parties to take far-reaching actions, not only with respect to acid rain but also with respect to several other air pollution problems (Table  1 ). Emissions of all key air pollutants have been reduced significantly and for the most important acidifying compound, sulphur dioxide, emissions in Europe have decreased by 80% or more since the peaks around 1980–1990 (Fig.  1 ).

European emissions of sulphur dioxide (SO 2 —black), nitrogen oxides (NO x , calculated as NO 2 —green) and ammonia (NH 3 —blue) 1880–2020 (updated from Fig.  2 in Schöpp et al. 2003 )

In this paper, we present and discuss how the acid rain problem became a key environmental issue among industrial countries from the late 1960s and the following decades (Fig.  2 ). We view the problem from a science-to-policy interaction perspective, based on a Symposium in Stockholm in the autumn 2017 organised to manifest 50 years of international air pollution science and policy development. The Symposium involved both a testimony from a number of those involved in science and policy during the first decades of the history but also a discussion of what we have learned and how the experience can be used in the future. Further information about the symposium and its outcome can be found at http://acidrain50years.ivl.se .

The timeline of science and policy interactions in Europe and North America 1967–2018. (updated from Driscoll et al. 2012). Abbreviations not occurring in text. NAAQS: National Ambient Air Quality Standards under the US Clean Air Act; CCAA: Canadian Clean Air Act; RADM: Regional Atmospheric Deposition Model; MAGIC Model of Acidification of Groundwater in Catchments. It should be mentioned that Canada and US are both parties to the Air Convention and they have also signed and ratified most of its protocols

Our historical review will be limited to some of the issues brought up at the Symposium. For more information on the early history see Cowling ( 1982 ). A comprehensive description of the acid rain history has recently been published by Rothschild ( 2018 ). The history of the first 30 years of the science–policy interactions under the Air Convention is also described in Sliggers and Kakebeeke ( 2004 ).

Short historical review

The discovery and the early acid rain history.

In a deliberatively provocative article in the Swedish newspaper Dagens Nyheter in October 1967, entitled “An Insidious Chemical Warfare Among the Nations of Europe”, the Swedish scientist Svante Odén (Fig.  3 ) described a new and threatening environmental problem—Acid Rain. He pointed to the significant decrease in pH of rainwater and surface waters that had occurred over the previous decade and linked it to the large and increasing emissions of sulphur dioxide in Europe.

Svante Odén around 1970 (photo Ellis B. Cowling)

The discovery received immediate attention by the Swedish government and, a few weeks after Odén’s article, the minister of industry presented the issue at the Organisation for Economic Cooperation and Development (OECD), but it did not receive any political attention at that time. The issue was also brought up in OECD’s Air Pollution Management Committee by the Swedish delegate Göran Persson. Also, here the message was met by scepticism and the common opinion among the members in the committee was that sulphur dioxide was a local problem, which easily could be solved by tall stacks. It was not until Persson felt he was going to “loose the case” he “played his last card” and pointed to the observations of intercontinental transport of radioactivity from the Chinese nuclear bomb experiments. The opinion then changed and the meeting agreed that acid rain might be an issue to look into. From now on, OECD and the western world realised that air pollution might be a problem of international political dimensions.

Odén’s discoveries were to a large extent based on the regional precipitation networks that were running in Sweden and Europe. In 1947, the Swedish scientist Hans Egnér set up a Swedish network to investigate the importance of atmospheric deposition for the fertilisation of crops. In 1954, the network was expanded forming the European Air Chemistry Network (EACN) through initiatives by Egnér, Carl Gustav Rossby, and Erik Eriksson (Egnér and Eriksson 1955 ; see also Engardt et al. 2017 ). Data from these networks together with a Scandinavian surface water network set up by Odén in 1961 formed the basis for Odén’s observations on the ongoing acidification (Odén 1968 ).

Acid rain and many of its ecological effects were, however, recognised long before 1967–1968. In fact, many features of the acid rain phenomenon were first discovered by an English chemist, Robert Angus Smith, in the middle of the nineteenth century! In 1852, Smith published a detailed report on the chemistry of rain in and around the city of Manchester, England. Twenty years later, in a very detailed book titled “Air and Rain: The Beginnings of a Chemical Climatology”, Smith first used the term “acid rain” and enunciated many of the principal ideas that are part of our present understanding of this phenomenon (Smith 1872 ). Unfortunately, however, Smith’s pioneering book was substantially ignored by nearly every subsequent investigator.

In Norway salmon catches decreased substantially in the early 1900s and in 1927, Professor Knut Dahl hypothesised that acidification of surface waters could be a factor of importance for the extinction of fish. Later Alf Dannevig assumed that “The acidity of a lake is dependent on the acidity of the rainwater and the contributions from the soil” (Dannevig 1959 ).

Based on detailed field observations and experimental studies both in England and in Canada, beginning in 1955 and continuing through 1963, Eville Gorham and his colleagues built a significant foundation for contemporary understanding of the causes of acid precipitation and its impacts on aquatic ecosystems, agricultural crops, soils, and even human health (Gorham 1981 ; Cowling 1982 ). Thus, Gorham and his colleagues as well as Dahl and Dannevig had discovered major aspects of the causes of contemporary changes in the chemistry of atmospheric emissions and deposition and their effects on aquatic ecosystems.

But these pioneering contributions, like those of Smith a century earlier, were not generally recognised—neither by scientists nor by society in general. Gorham’s researches, like those of Smith a century before, were met by what Gorham himself acknowledged as a “thundering silence”, not only by the scientific community, but also by the public at large.

It was not until 1967 and 1968 when Svante Oden published both his deliberatively provocative article in Dagens Nyheter and his carefully documented Ecological Committee Report (Odén 1968 ) that the acid rain problem was brought to both public and scientific considerations. The report included a huge body of scientific and policy-relevant evidence that long-distance transport and deposition of acidifying pollutants were causing significant environmental and ecological impacts, even in countries far away from pollutant-emitting source areas in other countries.

The Swedish case study and the OECD project

Two years after Odén’s article, the Swedish government decided to prepare a “case study” as a contribution to the UN Conference on the Human–Environment in Stockholm 1972 (Royal Ministry of Foreign Affairs and Royal Ministry of Agriculture 1972 ). Bert Bolin at the Stockholm University was appointed chair of the study, which included Svante Odén, Henning Rodhe, and Lennart Granat as authors. The report included a broad environmental assessment of the sulphur emission problem including sources, atmospheric and surface water chemistry, and effects on ecosystems and materials. Finally, it also included scenarios and estimated costs for environmental damage and control; in fact it was probably the first full systems analysis of an environmental problem.

In the report, a first estimate was made of the relative contributions of domestic and foreign emissions to the sulphur deposition in Sweden (Rodhe 1972 ). Estimates were also made of the effects of sulphur emissions on excess mortality and showed that 50% of the Swedish lakes and rivers would reach a critical pH level within 50 years (assuming continuation of present emission trends). Even if some aspects of the report received criticism, the overall case study was well received by the UN conference and in its final report (see http://www.un-documents.net/aconf48-14r1.pdf ) regional air pollution was explicitly mentioned (§85) with a citation of the Swedish study.

The Swedish initiative in the OECD resulted in a collaborative project to investigate the nature and magnitude of the transboundary transport of emitted sulphur dioxide over Western Europe, in which 11 countries participated. To initiate the project, a Nordic organisation on scientific research, Nordforsk, was asked to plan and develop methodologies for the investigation. Scientists and institutions from Norway, Sweden, Denmark, and Finland established an expert group in April 1970, which became central for the development and implementation of the OECD project. The Norwegian Institute for Air Research (NILU) offered through its director Brynulf Ottar to coordinate the project. The project included emission inventories, measurements of atmospheric concentrations, and deposition, together with model development and application for the assessment of the transport. A key part of the model calculations was to prepare the so-called “blame matrices”, through which the transport of pollutants between countries could be quantified.

The main conclusion from the OECD project, published in 1977, was that “Sulphur compounds do travel long distances in the atmosphere and the air quality in any European country is measurably affected by emissions from other European countries” (OECD 1977 ). Even if there still were hesitations about the magnitude of the transport, the common opinion was that transboundary transport of air pollution is an issue that needs collaboration across national borders. These conclusions paved the road for a pan-European scientific collaboration on air pollution, the European Monitoring and Evaluation Programme (EMEP) starting in 1977. The findings from the project also formed the basis for the Air Convention (Table  1 ). EMEP was already from the beginning included in the Convention as a key element, strongly contributing to the scientific credibility of the policy work.

Threats to forests boosted the interest

In 1980, the German scientist Bernhard Ulrich warned that European forests were seriously threatened from atmospheric deposition of sulphur. From his long-term experiments in the Solling area, he concluded that the high deposition of atmospheric pollutants had seriously changed the soil chemistry (Ulrich et al. 1980 ). Ulrich pointed to the links between sulphur deposition and the release of inorganic aluminium. His findings became a policy issue not only in Germany but in Europe as a whole, and even in North America. The alarms—often exaggerated—went like a wildfire through media and changed many attitudes throughout Europe. Newspapers were filled with photos of dying forests, in particular from “The Black Triangle”, the border areas between Poland, East Germany, and Czechoslovakia, characterised by large combustion of brown coal with high sulphur content. Forest inventories showed crown thinning and other effects on forests, but it became difficult to finally determine that acid deposition was the (only) cause for the observed effects.

The increasing interest in regional air pollution also paved the way for the first international agreement on emission control under the Air Convention. As a start, countries with a large interest in taking actions formed a “club” under the Convention, aiming for a 30% reduction in emissions. This ambition then became the basis for the first emission reduction protocol, the Sulphur Protocol signed in 1985. While Germany and some other West European countries acted almost immediately on the alarms, the progress in emission control in Eastern Europe was very slow during the 1980s, even though several of these countries signed the protocol. In fact, substantial decrease in emissions did not take place in the East until after the break-down of the communist regimes and the industrial collapse around 1990.

Critical loads and advanced policies

One of the most well-known characteristics for the control of the acid rain problem is the concept of Critical Loads (Nilsson 1986 ; Nilsson and Grennfelt 1988 ). The Executive Body, the highest decision-making body of the Air Convention, decided in 1988 that new negotiations on the control of sulphur and nitrogen emissions should be based on critical loads, and all parties to the Convention were requested to prepare their own critical load maps. The Netherlands offered to take a lead and prepared mapping manuals and initiated an international network, which became crucial for the scientific and policy acceptance of the concept (Hettelingh et al. 1991 ; De Vries et al. 2015 ; Fig.  4 ). (The critical loads concept is further discussed later in the paper)

The outcome of emission control of SO2, NOx, and NH3 between 1990 and 2010 presented as maps on exceedance of critical loads of acidity. Such maps have played an important role for illustrating outcomes of future policies as well as of actions taken (from Maas and Grennfelt 2016 )

When critical loads became a basis for further protocols, Integrated Assessment Models (IAMs) offered a method to calculate how to achieve a prescribed ecosystem effect reduction in the most cost-effective way. A couple of different approaches were developed, but the model at the International Institute for Applied Systems Analysis (IIASA) became the official model on which the Second Sulphur Protocol signed in 1994 was agreed (Hordijk 1995 ).

When revising or developing a new protocol for nitrogen oxides the concept could, however, not be used in the same way as for sulphur and acid deposition, since the NO x emissions contributed to several effects and, in addition, a strategy would need to take additional compounds into account. Instead, a more advanced approach was suggested by which both several effects and several compounds could be considered simultaneously (Grennfelt et al. 1994 , Fig.  5 ). IIASA and other bodies under the Air Convention were asked to develop an integrated assessment model that fitted into a broader approach and a more comprehensive model was developed, which made it possible to simultaneously take into account the effects of acidic deposition, nitrogen deposition, and ozone—the so-called multi-pollutant, multi-effect approach. The calculations became the basis for the Gothenburg Protocol (GP) that was signed in 1999 (Amann et al. 1999 ). The GP and the parallel EU National Emissions Ceilings (NEC) Directive from 2001 outlined control measures for 2010 and beyond.

Links between sources and effects used as an illustration in the preparation of the Gothenburg Protocol. From Grennfelt et al. 1994

After 2000—Health effects and integration with other policies became main drivers

The basis for the GP was almost entirely ecosystem effects. Around 2000, however, public health effects from air pollution became increasingly important. Large epidemiological studies indicated that air pollution was a significant source of premature deaths and that particles were a main cause of the health effects (WHO 2018 ). When the European Commission started its work to revise the NEC directive, health effects became central and the Air Convention followed. Further studies have supported the role of air pollution for health effects and when the GP was finally revised in 2012, health effects dominated as a policy driver for the establishment of national emission ceilings, and for the first time particulate matter was included in an international protocol (Reis et al. 2012 ).

When considering further actions after signing the GP in 1999, it was realised that for some pollutants under the Air Convention, emission control needed to be considered over larger geographic scales than Europe and North America alone. Ozone was of particular importance, since long-term objectives in the form of critical levels and public health standards could not be reached without taking into account sources outside the areas considered so far. Future policies therefore needed to include the ozone precursors methane and to some extent carbon monoxide. A task force on Hemispheric Transport of Air Pollution (HTAP) was set up under the Convention in 2004, with a primary objective to quantify the intercontinental transport of pollutants. The outcome of its work clearly showed the importance of considering air pollution in a wider geographic perspective than had been done so far (Dentener et al. 2010 ).

Climate change has for more than a decade become an issue of increasing interest for air pollution science and policy. In many cases, the emission sources are the same and there are obvious co-benefits (and some trade-offs) in handling them together. One aspect that has received large interest is the option to decrease short-term temperature increase through control measures directed towards atmospheric pollutants that also contribute to the warming of the atmosphere, in particular black carbon and methane (for methane both by itself but also as a tropospheric ozone precursor) (Ramanathan et al. 2001 ). Compounds contributing to both air pollution effects and to the radiation balance in the atmosphere have been named Short Lived Climate Pollutants (SLCPs). SLCPs thus also include compounds that are cooling the atmosphere, i.e. small secondary aerosols, e.g. sulphate particles. Recent research has focused on a better understanding of these compounds’ contribution to both air pollution and climate as well as on opportunities for selective control of these compounds (e.g. Sand et al. 2016 ).

Reactive nitrogen species are another group of compounds that has received increased attention after the turn of the century. Around 2006 several initiatives were taken in Europe, including a special task force on Reactive Nitrogen under the Air Convention, a large-scale EU project on nitrogen, and the preparation of a European Nitrogen Assessment (Sutton et al. 2011 ). Here nitrogen was considered both as a traditional atmospheric pollutant and within a societal and industrial context. A cascade perspective, where one fixed nitrogen molecule could contribute to a series of effects before it returns to molecular nitrogen again, was introduced (Galloway et al. 2003 ). The studies have pointed to the importance of the agricultural sector for the intensification of reactive nitrogen cycling, determined by food production mechanisms and dietary choices.

North America

In North America, the acid rain problem developed to a large extent in parallel with the situation in Europe. Lake acidification became already from the beginning a main driver, and monitoring programmes were set up both in the United States and Canada (Driscoll et al. 2010 ). The US National Atmospheric Deposition programme (NADP) started in 1976 and is still running. Both countries have taken part in the Air Convention activities and have signed most of the protocols and achieved decreases in SO 2 emissions of the order of 80% between 1980 and 2015. The US has however taken a different approach with respect to policy in comparison to Europe. Instead of developing a strategy based on integrated assessment modelling, it was decided to establish an emissions trading programme for the large electric generation sources under the Clean Air Act (See also UNECE 2016 ).

Characteristics of the science–policy interactions

In this section we will, from a science–policy perspective, briefly discuss some characteristics of the history of acid rain and transboundary air pollution that have become central for the international collaboration, not only on air pollution but also for international environmental collaboration in general. We will bring up monitoring, modelling, and data collection (including field experiments and long-term studies carried out in order to understand and quantify effects to ecosystems), development of bridging concepts that have served the implementation of strategies, and finally the dynamics in the science–policy interactions.

Monitoring, modelling, and data collection

Monitoring of atmospheric concentrations, deposition, and ecosystem effects has been a key for understanding the causes, impact, and trends in acid rain, both in Europe and North America and later in other geographic areas (Table  2 ). The original EMEP network has since the start over 40 years ago formed a broad atmospheric monitoring system. The originally established simple monitoring stations have over time been complemented with more advanced monitoring, and some stations are today advanced atmospheric chemistry platforms with continuous collection of a multitude of atmospheric parameters (Fig.  6 ). The EMEP database is nowadays widely used for a variety of scientific purposes including computation of long-term trends, exposure estimates, and as a basis for modelling. EMEP has also become a model for monitoring networks related to other geographical regions, conventions, and purposes. One example is the acid deposition monitoring network in East Asia (EANET). It is obvious that having a qualified centre for data collection and storage, standardisation, and intercalibration of methods has served the international policy system extremely well. Its open nature is part of the success. The financial support to EMEP, regulated through a separate protocol, has been fundamental for the development and progress of the monitoring activities.

Atmospheric monitoring stations have been of importance for understanding the long-range transport and chemical conversions of atmospheric pollutants. Pallas air pollution background station in Northern Finland (Photo Martin Forsius)

Monitoring of air pollution effects in a systematic way under the Air Convention started a few years later than EMEP and was organised through so-called International Cooperative Programmes (ICPs). Separate programmes were set up for forests, waters, vegetation (primarily ozone), materials, and integrated monitoring. A separate ICP was set up for developing critical load methodologies and coordinating European-scale mapping activities (ICP Modelling and Mapping). The ICPs are of great importance for general understanding of the magnitude and geographical distribution of the effects and for showing how decreases in emissions have led to beneficial conditions in ecosystems and decreased material corrosion (Maas and Grennfelt 2016 ). Ecosystem monitoring is also important for the development and verification of ecosystem models. Since their start, the responsibility for the ICPs has been taken by different parties of the Air Convention (Table  2 ). The distributed responsibility has been of large importance for the establishment of networks of monitoring sites among the Convention parties, but the system has not had a stable financial support in the same way as for EMEP. This has resulted in the lack of a common source for easily accessible data or adequate resources for standardisation and intercalibration.

Monitoring and other data collection (i.e. emissions and critical loads) under the Air Convention are responsibilities of every country, and data are then used for the assessments on the Convention level as well as for the development of EU air pollution policies. The bottom-up process in data collection is important for the development of national expertise and, not the least, for the establishment of national policies. In this way, direct communication links between the science and the policy levels within countries have evolved.

Numerical modelling of atmospheric pollution is also a long-term commitment under EMEP. The atmospheric chemistry models are necessary for the understanding of the nature of transboundary transport but also to make budget estimates of the exchange of pollutants over Europe and North America, and later on a hemispheric scale. The Meteorological Synthesizing Centre West at the Norwegian Meteorological Institute together with the Eastern Centre in Moscow took the lead in this work. In addition to calculating transboundary fluxes, the centres are important for coordinating modelling efforts done by other groups, forming a basis for scrutinising models and support further modelling.

Field experiments and long-term studies—a way to understand processes and trends, and to visualise the problems

Some of the most important and reliable findings regarding acid rain and its effects on ecosystems emanate from long-term field experiments. These experiments, which are known from the sites where they are run, include Hubbard Brook (US), Solling (Germany), Risdalsheia (Norway) and Lake Gårdsjön (Sweden) (Fig.  7 ). The studies there have shown how acid deposition and the impact of other air pollutants have changed the ecosystems, but also how ecosystems respond to decreased emissions (e.g. Wright et al. 1988 ; Likens et al. 1996 ). A central feature in all these field experiments was the establishment of ion budgets, from which the chemical effects on acid deposition can be analysed and understood (Reuss et al. 1987 ).

Field experiments have played an important role for the overall understanding of the interactions between atmospheric deposition and ecosystem effects. The photo illustrates the covered catchment experiment to study the recovery of ecosystems at reduced emissions in Risdalsheia Norway (Photo NIVA)

In the intense research period during the 1970s and 1980s, a number of large-scale research programmes and experiments of temporary nature were set up, some of them in connection with the above-mentioned sites. The first research programme of some magnitude was the Norwegian programme “Acid precipitation—effects on forest and fish” (SNSF), which run between 1972 and 1980 (Overrein et al. 1981 ). At that time the scientific understanding was limited, and the programme received a lot of attention. The results were important for the general acceptance that long-distance transport of sulphur caused acidification of surface waters, with a serious die-off of fresh water fish populations (salmon and trout) as a main consequence. On the other hand, the studies on Norwegian forests did not give any significant evidence for acid rain effects. The SNSF project was a joint effort across disciplinary and organisational boundaries, with scientists mainly from the research institute sectors outside of traditional academia. This project served as a model for later research programmes and provided educational opportunities for a new generation of scientists working together on all aspects of the acid rain issue—emissions and their control, atmospheric transport and deposition, impact on ecosystems, health and materials, and finally development of pollutant-control policies.

The long-term field experiments served another important task. The sites became exhibition platforms, at which policymakers, experts, scientific journalists, and leaders of non-governmental organisations (NGOs) and others can be informed about the problem directly on site. During the most intense period in the 1980s and early 1990s, politicians and industry leaders, often directly involved in decisions on the highest levels, visited many of these experimental sites. For example, US congress members travelled across Europe to see and understand the issue in preparation for the 1990 amendment of the Clean Air Act.

Bridging concepts and approaches

Concepts developed, such as critical loads and similar approaches, formed links between science and policy, and were essential for the understanding and scientific legitimacy of the policy measures. These concepts also formed a basis for priority setting in agreements under the Convention and the EU, but also to some extent for national policies. Even “acid rain” can be considered as a bridging concept. While the acidity from sulphur and nitrogen compounds is threatening ecosystems through a chemical change, the expression also gives the impression of a threat to the life-giving rain, a fundamental necessity for life on Earth.

The quantification of transboundary fluxes was very important politically. The establishment of national budgets and so-called blame matrices formed the first bridging concept. The development of mathematical models to calculate source–receptor relations was a scientific challenge but when the annual tables were prepared showing the interdependence between countries with respect to atmospheric emissions and deposition, they served as an important basis for the need for common action. Anton Eliassen, the leader of the modelling centre at the EMEP Meteorological Synthesising Centre West (MSC-W) during many years (the Eastern center is in Moscow—MSC-E), was key to this development as well as for the communication of the results to policymakers.

As earlier mentioned, critical loads played an outstanding role for the development of the more advanced strategies leading to the Second Sulphur Protocol and the GP. Critical loads formed a successful link between science and policy that became crucial for the negotiations and agreements. The concept, first discussed in 1982, was taken from the original idea to application quite quickly during the 1980s. The Swedish expert Jan Nilsson was a key leader for the success of the concept, and the Nordic Council of Ministers played a unique role for forming the links between science and policy. Through a series of workshops involving both key scientists and key policymakers, the concept gained the legitimacy on which policies were developed. According to Jan Nilsson, it all started with requests from both industry and negotiators to have a sounder base for emission control, something that could express the long-term objectives for emission control policies. The concept was first met by scepticism, not least from scientists, but after a couple of workshops, the interest turned around and the concept became widely accepted (Nilsson 1986 ; Nilsson and Grennfelt 1988 ). When critical loads were included in the plans for the next rounds of the sulphur and nitrogen protocols in 1988, it changed the way the Air Convention operated.

The application of the critical loads concept has encouraged intense research over several decades where the main objective has been to find simple chemical parameters that can mimic the (often biological) real effects or effect risks. For lake acidification, where the effects of dissolved aluminium on fish often were chosen as the main biological effect, the acidity of the water, mostly expressed as acid neutralising capacity (ANC), is used (e.g. Henriksen et al. 1989 ; Forsius et al. 2003 ; Posch et al. 2012 ). For forests, where the toxicity of aluminium to tree roots is considered as critical, the Al 3+ to Ca 2+ ratio in soil water has become the main effect parameter (Sverdrup et al. 1990 ; de Vries et al. 1994 ).

Integrated assessment modelling (IAM) also has been a bridging concept. The idea of applying systems analysis goes back to the work at IIASA in the beginning of 1980s. A conceptual model was formulated by Joseph Alcamo, Pekka Kauppi, and Maximilian Posch for the interactions between emissions, their control (including costs), and the effects on ecosystems (Alcamo et al. 1984 ). Their work of bringing together the scientific knowledge to a comprehensive systems analysis tool formed a new way of framing environmental policies. Under the leadership of Leen Hordijk, the new idea was introduced to and accepted by the policy side, which had asked for more targeted methods for policies than simple percentage decreases in amounts of emissions. IAMs as a policy-supporting concept was then taken further by Markus Amann, who led the development of the more advanced RAINS (later GAINS) models that were used as a basis for the GP and later agreements (Amann et al. 2011 ). From the strategies strictly directed at ecosystem effects, the approach is now widened to include health effects, local air pollution impact, climate policies, and reactive nitrogen.

All the bridging concepts are to varying degrees dependent on underlying models, assumptions, and simplifications. For these to be accepted among policymakers, it is important to keep transparency and confidence in the underlying data and to scientifically evaluate and scrutinise them. This is particularly important for the IAMs, which are the final step in a chain of inputs (Fig.  8 ). The models have often been criticised, not least from industry and other stakeholders that are questioning the priorities that result from the IAM calculations. IIASA, as a provider of the model calculations, has, however, been transparent, and countries and stakeholders have always had the option to re-check data and take this into account when developing their own negotiation positions.

The scientific support to regional air pollution policies consists today of a series of steps. The policy side may often only see the integrated assessment step and not realise that the legitimacy of the use of scientific support builds on an advanced system of underlying research and development

Forming science–policy credibility

In all interactions between science and policy, it becomes crucially important to maintain scientific credibility. The close involvement of scientists has been a signature of the Air Convention. Scientists have always had a role at the policy meetings, communicating results from basic scientific research over outcomes of monitoring and inventories to presenting options for control strategies. Scientists have in this way taken the responsibility to move scientific knowledge into the policy system and presenting results in a way that has been understandable and useful for the policy work. The role of the scientists has been as honest brokers , not that of issue advocates to follow the terminology of Pielke ( 2007 ). The leadership from the policy side and its sensitivity to changes in the underlying science and observations of new problems have also been important, and have resulted in repeated changes in the framings of the Air Convention to adapt to new situations: going from an initial framing around sulphur and acidification, through extension to eutrophication, human health, materials, crops, biological diversity, and finally to links to climate, urban air quality, and societal changes. A balanced interplay between the two communities has in this way been developed and maintained over time.

Another factor is the building of networks. The strong networks of scientists and policymakers pushed the politicians. The whole field of international diplomacy during these four decades of the Convention is built on incremental developments forming protocols of increasing capability to solve specific environmental issues by cutting emissions in a cost-effective way.

Future challenges

New approaches necessary.

International air pollution control is by many considered as a success story. However, the success is in many ways limited to Europe and North America and a few additional industrialised countries (including Japan and Australia), where emissions of sulphur dioxide, nitrogen oxides, VOCs, and some other compounds have been decreased significantly (Maas and Grennfelt 2016 ). But even in the areas, where air pollution has been a top priority for several decades, air pollution remains a problem. Ecosystem effects, which were the main reason for the establishment of the Convention, are to some extent reduced, but the acidification effects of historical emissions will remain for decades (Wright et al. 2005 ; Johnson et al. 2018 ) and the emissions of ammonia have so far only been reduced by 20–30% in Europe and even less in North America. Looking at health effects, it is difficult to talk about success, when hundreds of thousands of inhabitants on both continents are predicted to meet an earlier death due to air pollution.

But the problem is even larger and more urgent when looking outside the traditional industrialised world. The focus is today on the large urban regions in the countries that are facing rapid population growth and industrialisation. Although large efforts now are being made to decrease sulphur emissions in China—the world’s leading sulphur emitter—major challenges remain. In India and several other countries, sulphur emissions are still increasing. Estimates indicate that more than four million people die prematurely due to outdoor air pollution globally ( https://www.who.int/airpollution/ambient/health-impacts/en/ ). It is assumed that fine particles (PM2.5) are a main cause for the health effects. The new and great challenge is therefore to control air pollution in relation to health risks, in particular by decreasing exposure to the small particles.

There is, however, a risk that control measures will only to a limited extent focus on the right sources and the right measures. In Paris, several air pollution episodes with high concentrations of particles have occurred during recent years. At first, these episodes were considered to be caused essentially by local emissions. More thorough analysis has, however, shown that they were to a large extent caused by regional emissions and buildup of high concentrations over several days when urban emissions of oxides of nitrogen from traffic mix with ammonium emissions from surrounding agricultural areas to form particulate nitrate. Similar situations are also often encountered in urban regions in developing countries, e.g. by agricultural waste burning, and need to be considered. Air pollution problems are, as previously mentioned, also linked to intercontinental and hemispheric scales.

It is also obvious that the research communities within air pollution and climate change need to work more closely together. Health aspects are of importance both from air pollution and climate change perspectives, and heat waves carry poor air quality as winds are often very low and the atmospheric boundary layer stagnant. During heat waves, the soil and vegetation dry up and increase the likelihood of fires, which also can cause severe air pollution, as seen in wildfires around the world (e.g. California in 2018).

Despite the large progress in atmospheric and air pollution science, basic questions still need further investigations to develop the best policies. Such areas include a better understanding of health effects from air pollution, nitrogen effects to ecosystems, and air pollution interactions with climate through carbon storage in ecosystems and impacts on radiation balances. Modelling is a scientific area where much progress has been made and where increased computer power, as in climate change research, has allowed integration of atmospheric chemistry into the climate models formulated as Earth system models, coupling the atmosphere, ocean, the land surface, cryosphere, biogeochemical cycles, and human activities together. This has allowed studying air pollution and climate change simultaneously. The modelling approach can be further developed when observations are designed to map Earth system component boundaries to understand and quantify the flows and interactions between different compartments, including terrestrial and aquatic ecosystems. Air pollution should be an integrated part of such models. In this context, global-scale concepts such as “planetary boundaries” and “trajectories of the Earth system vs. planetary thresholds” have been developed (Rockström et al. 2009 ; Steffen et al. 2018 ).

Solutions are available; driving forces and investments are lacking

In 2016, the Air Convention launched a scientific report “Towards Cleaner Air”, in which the actual air pollution situation within the UNECE region was updated (Maas and Grennfelt 2016 ). The report also presented future challenges and ways forward to solve the air pollution problems. It also showed that solutions are available for most of the identified problems at affordable costs below the health and ecosystem benefits of the control actions.

Even if solutions are available, many parts of the world are facing large problems in implementing them. There are several reasons, but often there is a lack of knowledge and resources. This is particularly true in many developing countries. Another reason is the lack of political interest. Air pollution is still not of top priority among politicians, even if there is overwhelming evidence that air pollution is one of the most common causes of shortened life expectancies. Another reason may be that other interests (e.g., industry and agriculture) are forming strong lobbying forces delaying actions.

Air pollution is a problem that cannot be seen in isolation. Future policies need to take into account climate change and climate change policies. Whereas some air pollutants—in particular black carbon particles—contribute to warming, others, including sulphate particles, tend to cool the climate. A reduction in sulphur dioxide emissions, although highly desirable from health and ecosystems perspectives, will therefore contribute to warming. On the other hand, a reduction of black carbon will be a win–win solution. It is also important to see air pollution control in the perspective of sector policies, such as energy, agriculture, transportation, and urban planning in order to meet the challenges to decrease air pollution problems.

Internationally coordinated actions and infrastructures are keys for success

The perspective of international cooperation on air pollution is changing. Policy development is no longer limited to long-range transport in line with that developed under the Air Convention. The ranking of air pollution as a top ten cause of premature deaths in the world has given high priority to the issue within fora such as the WHO and UN Environment. Both organisations have adopted resolutions calling for actions (WHO 2015 ; UN Environment 2017 ). Additional initiatives are taken by other organisations, such as the World Meteorological Organisation (WMO), the Climate and Clean Air Coalition (CCAC), and the Arctic Monitoring and Assessment Programme (AMAP). WMO is particularly important as a global technical agency for weather and climate observations, research and services, and it is rapidly developing its regional and global capacities in Earth system observations, modelling, and predictions to the benefit of mitigating a range of environmental threats and for global use. The research is done in large programmes like Global Atmosphere Watch (GAW) and the World Weather Research Programme (WWRP). Even if the starting point and modes of action can be different, all initiatives are aiming for the same goal, cleaner air. It is also worth mentioning the initiative taken by the International Law Commission, under which a proposal for a Law for the Protection of the Atmosphere has been prepared ( http://legal.un.org/ilc/summaries/8_8.shtml ) but in the current international atmosphere there is a lack of political support to implement it. Our hope is that the situation will change soon—the initiative is too important to fail.

The UN has put forward a very strong agenda in order to reach the Sustainable Development Goals (SDGs), and air pollution is an integral part of several of the SGDs, like goal No 2: No Hunger, No 3: Good health and well-being, No 6: Clean Water, No 7: Affordable and clean energy, No 9: Industry, innovation and infrastructure, No 11: Sustainable cities and communities, No 13: Climate action, No 14: Life below water, No 15: Life on Land, No 16: Peace and Justice, and No 17: Partnerships for the Goals. The approach taken to develop multiple pollutant—multiple impacts protocols under the Air Convention can serve as important learning ground to meet the ambitions of many of the SDGs. Air pollution plays an integral role in the evolution of the food production and ecosystem services, the health of the population, the shape of the energy and transportation systems, and the availability of clean water. Climate change is a very significant common and cross-cutting factor.

The Air Convention has taken some steps in promoting air pollution on a wider scale. Due to its long history and well-developed structure, it has taken a role of making sure that international organisations having air pollution on its agenda are aware of each other and to invite to further collaboration and development. Initiatives are taken both within the formal Convention structure and through dedicated workshops (UNECE 2018 ; Engleryd and Grennfelt 2018 ). The approach developed under the Air Convention, which has proven successful in linking scientific evidence, monitoring, and integrated assessment modelling directed towards cost-effective solutions, may also serve as a working model for environmental problems in other fields.

These new international initiatives have a strong emphasis on policy development. The experience from the 50 years of international air pollution development is the value of well-defined scientific objectives and activities supporting policy. The increased interest from WHO and UN Environment is welcome and there are expectations of an active role from these organisations in combatting the situation in many parts of the world. However, for these organisations, air pollution is just one of several priority areas, and priorities may change. Further, none of these organisations are likely able to set up advanced infrastructures with respect to emission inventories, monitoring, and research. Here WMO needs to live up to its mission and capitalise on global research and development efforts and improve the global operational capability to observe, analyse, and forecast the development of the Earth system and its components, air pollution being an important part. This is in line with the WMO strategic plan and with fast growing capabilities in some countries and in global centres like The European Centre for Medium Range Weather Forecast (ECMWF). WMO, through GAW, is also developing a research-driven operational system (IG3IS) for top-down determination of greenhouse gas emissions, to complement the usual bottom-up-based inventories where emission factors and fuel consumption or production statistics form the basis for the emission estimates ( https://library.wmo.int/doc_num.php?explnum_id=4981 ). The Air Convention and the science support for the policy work there has been a model for the WMO ambitions on a global basis. However, current investments in these new capabilities are not enough to get the societal return they would offer.

Therefore, we see a need for developing long-lasting infrastructures that can continuously develop science-based control policy options, potentially as part of a wider network of global observatories for comprehensive monitoring of interactions between the planet’s surface and atmosphere (Kulmala 2018 ). Such a network should be able to support policies from local to the global levels. The challenge is how to organise and raise resources for scientific support on a wider scale. Financial institutions such as the World Bank and/or regional banks may step in and make sure that control measures and investments are made on a sound basis with respect to global air pollution.

There is also a need to mobilise new generations of scientists, scientists that are willing to cross boundaries and focus on thematic problems and to build legitimacy among policymakers (e.g. Bouma 2016 ). Today we have more developed and stronger political institutions to handle environmental problems, which may make it harder for scientists and individuals to influence and make a difference. It is also important to mobilise new generations of dedicated policymakers. Unfortunately, we also see that politicians often are questioning science and seeing science as just a special interest. Public awareness may be a key for forming stronger interests and put pressure on decision-makers. During the acid rain history, NGOs played an important role in driving the awareness at a wider scale than local or national actions and could be important for a more global movement towards cleaner air. We also see the need for a deeper responsibility not only from politicians but also from industry. The so-called “diesel gate” exposed the cynic view from parts of the industry to peoples’ health, which hopefully will not occur in the future. Instead we hope that it was an eye-opener and that industry instead can play a role as a forerunner and a positive power for a cleaner atmosphere.

Final remarks

The Acid Rain history taught us that when science, policy, industry, and the public worked together, the basis was formed for the successful control of, what was considered, one of the largest environmental problems towards the end of the last century. We learnt from experience that science-based policy advice worked well when the best available knowledge was provided, and used to understand the specific problems, generate, and evaluate the policy options and monitor the outcomes of policy implementation.

However, the world does not look the same today, and we cannot just apply the ways the international science community worked together then on today’s problems. But there are lessons to be learnt. Most important is the building of mutual trust between science advisers and policymakers, and that both communities are honest about their values and goals. In this way, a fruitful discussion around critical topics within society can be formed. The advice works best when it is guided by the ideal of co - creation of knowledge and policy options between scientists and policymakers (SAPEA 2019 ).

Amann M., I. Bertok, J. Cofala, F. Gyarfas, C. Heyes, Z. Klimont, and W. Schöpp. 1999. Integrated assessment modelling for the protocol to abate acidification, eutrophication and ground-level ozone in Europe, Lucht & Energie 132, November 1999.

Amann, M., I. Bertok, J. Borken-Kleefeld, J. Cofala, C. Heyes, L. Höglund-Isaksson, Z. Klimont, B. Nguyen, et al. 2011. Cost-effective control of air quality and greenhouse gases in Europe: Modeling and policy applications. Environmental Modelling & Software 26 (12): 1489–1501.

Article   Google Scholar  

Alcamo, J., P. Kauppi, M. Posch and E. Runca. 1984. Acid rain in Europe: A framework to assist decision making. Working paper WP-84-32, International Institute for Applied Systems Analysis, Laxenburg, Austria.

Bouma, J. 2016. Implications of the nexus approach when assessing water and soil quality as a function of solid and liquid waste management. In Environmental resource management and the nexus approach , ed. H. Hettiarachchi and R. Ardakanian, 179–209. New York: Springer.

Chapter   Google Scholar  

Cowling, E.B. 1982. Acid precipitation in a historical perspective. Environmental Science & Technology 16: 110A–123A.

Article   CAS   Google Scholar  

Dannevig, A. 1959. Influence of precipitation on river acidity and fish populations. Jeger og Fisker 3: 116–118.

Google Scholar  

Dentener, F., T. Keating, and H. Akimoto. 2010. Hemispheric transport of air pollution, part A. air pollution studies no. 17, Convention on long-range transboundary air pollution, UNECE.

De Vries, W., G.J. Reinds, and M. Posch. 1994. Assessment of critical loads and their exceedance on European forests using a one-layer steady-state model. Water, Air, and Soil Pollution 72: 357–394.

De Vries, W., J.-P. Hettelingh, and M. Posch, eds. 2015. Critical loads and dynamic risk assessments: Nitrogen, acidity and metals in terrestrial and aquatic ecosystems. Environmental pollution series, Vol. 25. Dordrecht: Springer. ISBN 978-94-017-9507-4; https://doi.org/10.1007/978-94-017-9508-1 .

Driscoll, C.T., E.B. Cowling, P. Grennfelt, J.M. Galloway, and R.L. Dennis. 2010. Integrated assessment of ecosystem effects of atmospheric deposition: Lessons available to be learned. EM Magazine , November 2010: 6–13.

Engleryd, A. and P. Grennfelt. 2018. Saltsjöbaden VI workshop. Clean air for a sustainable future—goals and challenges. Nordic Council of Ministers, TemaNord 2018:540, Copenhagen, ISSN 0908-6692. http://saltsjobaden6.ivl.se/finalreport.4.14bae12b164a305ba11c38f.html .

Egnér, H., and E. Eriksson. 1955. Current data on the chemical composition of air and precipitation. Tellus 7: 134–139.

Engardt, M., D. Simpson, M. Schwikowski, and L. Granat. 2017. Deposition of sulphur and nitrogen in Europe 1900-2050. Model calculations and comparison to historical observations. Tellus B 69: 1328945. https://doi.org/10.1080/16000889.2017.1328945 .

Forsius, M., J. Vuorenmaa, J. Mannio, and S. Syri. 2003. Recovery from acidification of Finnish lakes: Regional patterns and relations to emission reduction policy. Science of the Total Environment 310: 121–132.

Galloway, J.N., J.D. Aber, J.W. Erisman, S.P. Seitzinger, R.W. Howarth, E.B. Cowling, and B.J. Cosby. 2003. The nitrogen cascade. BioScience 53 (4): 341–356.

Grennfelt, P., Ø. Hov, and R.G. Derwent. 1994. Second generation abatement strategies for NO X , NH 3 , SO 2 and VOC. Ambio 23: 425–433.

Gorham, E. 1981. Scientific understanding of atmosphere-biosphere Interactions: A historical review. Chapter 2. In Toward a better understanding of the ecological consequences of fossil fuel combustion . National Research Council, 9–21. 1981. Washington, DC: The National Academies Press. https://doi.org/10.17226/135 .

Henriksen, A., L. Lien, B.O. Rosseland, T.S. Traaen, and I.S. Sevaldrud. 1989. Lake acidification in Norway—present and predicted fish status. Ambio 18: 314–321.

Hettelingh, J.-P., R.J. Downing, and P.A.M. de Smet. 1991. Mapping critical loads for Europe, CCE Status Report 1 1991, Coordination Center for Effects, National Institute of Public Health and the Environment (RIVM), Bilthoven, The Netherlands.

Hordijk, L. 1995. Integrated assessment models as a basis for air pollution negotiations. Water, Air, and Soil pollution 85: 249–260.

Johnson, J., E. Graf Pannatier, S. Carnicelli, C. Cecchini, N. Clarke, N. Cools, K. Hansen, H. Meesenburg, et al. 2018. The response of soil solution chemistry in European forests to decreasing acid deposition. Global Change Biology 24: 3603–3619.

Kulmala, M. 2018. Build a global Earth observatory. Nature 553: 21–23.

Likens, G.E., C.T. Driscoll, and D.C. Buso. 1996. Long-term effects of acid rain: Response and recovery of a forested ecosystem. Science 272: 244–246.

Maas R. and P. Grennfelt, eds. 2016. Towards cleaner air. Scientific assessment report 2016. EMEP steering body and Working Group on effects of the convention on long-range transboundary air pollution, Oslo.

Nilsson J., ed. 1986. Critical loads for nitrogen and sulphur. Report from a Nordic working group, Nordic Council of Ministers, Miljø rapport 1986:11, Stockholm.

Nilsson, J. and P. Grennfelt, eds. 1988. Critical loads for sulphur and nitrogen. Report of a workshop held in Skokloster, Nordic Council of Ministers, Miljø rapport 1988:15, Stockholm.

Odén, S. 1968. The acidification of air precipitation and its consequences in the natural environment. Bulletin Ecological Research Commission. NFR. Translation Consultants Ltd., Arlington VA.

OECD. 1977. The OECD programme on long range transport of air pollutants . Paris: Measurements and Findings.

Overrein, L.N., H.M. Seip, and A. Tollan, eds. 1981. Acid precipitation–effects on forest and fish: Final report of the SNSF-project 1972-1980. Oslo Norway.

Pielke, R.A. Jr. 2007. The honest broker. Making sense of science in policy and politics. Cambridge: Cambridge University Press.

Posch, M., J. Aherne, M. Forsius, and M. Rask. 2012. Past, present and future exceedance of critical loads of acidity for surface waters in Finland. Environmental Science and Technology 46: 4507–4514.

Ramanathan, V., P.J. Crutzen, J.T. Kiehl, and D. Rosenfeld. 2001. Review paper: Aerosols, climate, and the hydrological cycle. Science 294: 2119–2124.

Reis, S., P. Grennfelt, Z. Klimont, M. Amann, H. Apsimon, J.-P. Hettelingh, M. Holland, A.-C. LeGall, et al. 2012. From acid rain to climate change. Science 338 (6111): 1153–1154.

Reuss, J.O., B.J. Cosby, and R.F. Wright. 1987. Chemical processes governing soil and water acidification. Nature 329: 27–32.

Rockström, J., W. Steffen, K. Noone, et al. 2009. A safe operating space for humanity. Nature 461: 472–475.

Rodhe, H. 1972. A study of the sulfur budget for the atmosphere over Northern Europe. Tellus 24: 128–138.

CAS   Google Scholar  

Rothschild, R.E. 2018. Poisonous skies. Acid rain and the globalization of pollution . Chicago: University of Chicago Press. ISBN 9780226634852.

Royal Ministry of Foreign Affairs and Royal Ministry of Agriculture. 1972. Air pollution across national boundaries. The impact on the environment of sulfur in air and precipitation. In Sweden’s case study for the United Nations’ Conference on the Human Environment, Stockholm.

Sand, M., T.K. Berntsen, K. von Salzen, M.G. Flanner, J. Langner, and D.G. Victor. 2016. Response of Arctic temperature to changes in emissions of short-lived climate forcers. Nature Climate Change 6: 286–289. https://doi.org/10.1038/nclimate2880 .

SAPEA. 2019. Making sense of science for policy under conditions of complexity and uncertainty. Science Advice for Policy by European Academies, 1–186, Berlin. https://doi.org/10.26356/MASOS .

Schöpp, W., M. Posch, S. Mylona, and M. Johansson. 2003. Long-term development of acid deposition (1880–2030) in sensitive freshwater regions in Europe. Hydrology and Earth System Sciences 7: 436–446. https://doi.org/10.5194/hess-7-436-2003 .

Sliggers, J. and W. Kakebeeke, eds. 2004. Clearing the air. 25 years of the convention on long-range transboundary air pollution. United Nations Economic Commission for Europe, Geneva 1–167.

Smith, R.A. 1872. Air and Rain, the Beginnings of a Chemical Climatology . London: Longmans Green.

Steffen, W., J. Rockström, K. Richardson, T.M. Lenton, C. Folke, D. Liverman, C.P. Summerhayes, A.D. Barnosky, et al. 2018. Trajectories of the earth system in the anthropocene. PNAS 115 (33): 8252–8259. https://doi.org/10.1073/pnas.1810141115 .

Sverdrup, H., W. de Vries, and A. Henriksen. 1990. Mapping critical loads, Nord 1990:98 . Copenhagen: Nordic Council of Ministers.

Sutton, M.A., C.M. Howard, J.W. Erisman, G. Billen, A. Bleeker, P. Grennfelt, H. van Grinsven, and B. Grizzetti (eds.). 2011. The European nitrogen assessment . Cambridge: Cambridge University Press.

Ulrich, B., R. Mayer, and P.K. Khanna. 1980. Chemical changes due to acid precipitation in a loess‐derived soil in Central Europe. Soil Science 130: 193–199.

UNECE. 2016. Towards cleaner air. Scientific assessment report 2016: North America. United Nations, Geneva. http://www.unece.org/index.php?id=42947&L=0 .

UNECE. 2018. Report from 38th session of the executive body for the convention on long-range transboundary air pollution Geneva 10–14 December 2018, Annex, 18–21, http://www.unece.org/fileadmin/DAM/env/documents/2018/Air/EB/ECE_EB.AIR_142-1902903E.pdf .

UN Environment. 2017. Preventing and reducing air pollution to improve air quality globally on air quality. Third UN Environment Assembly, 4–6 December 2017, Resolution 8. https://papersmart.unon.org/resolution/uploads/k1800222.english.pdf .

WHO. 2015. Resolution WHA68.8 health and the environment: addressing the health impact of air pollution. 68th World Health Assembly World Health Organisation, http://apps.who.int/gb/ebwha/pdf_files/WHA68/A68_R8-en.pdf .

WHO. 2018. https://www.who.int/en/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health .

Wright, R.F., E. Lotse, and A. Semb. 1988. Reversibility of acidification shown by whole-catchment experiments. Nature 334: 670–675.

Wright, R.F., L. Camarero, B.J. Cosby, R.C. Ferrier, M. Forsius, R. Helliwell, A. Jenkins, J. Kopáček, et al. 2005. Recovery of acidified European surface waters. Environmental Science and Technology 39: 64A–72A.

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Open access funding provided by The Swedish Environmental Protection Agency. The Symposium could not have been arranged and this paper written without financial support from the Nordic Council of Ministers, the Swedish Environmental Protection Agency, the Mistra Foundation, and other organisations and institutes in the Nordic countries. We are also grateful to all participants of the Symposium and their contributions with background material for this paper. We also thank the two anonymous reviewers of the manuscript. Their comments greatly improved the quality of this paper.

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Grennfelt, P., Engleryd, A., Forsius, M. et al. Acid rain and air pollution: 50 years of progress in environmental science and policy. Ambio 49 , 849–864 (2020). https://doi.org/10.1007/s13280-019-01244-4

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Lead Scientist(s) : Dr. Gene E. Likens

Acid rain is a popular term for the atmospheric deposition of rain, snow, sleet, hail, acidifying gases and particles, as well as acidified fog and cloud water. Dr. Gene E. Likens discovered acid rain in North America when working with colleagues at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire.

"We knew from the very first samples of rain we collected in 1963, that it was very acid, but we didn't know the cause or extent of the environmental problem"

said Likens. The pH of these first samples averaged about 4.1 and was often much lower, up to 100 times more acidic than unpolluted rain.

The pH scale indicates the acidity or base of a solution, like degrees Celsius represent the temperature. Each unit on the pH scale represents a 10-fold difference, so a pH of 4 is 10 times more acid than a pH of 5. Beer has an acidic pH of 4, milk has a neutral pH of 7, and baking soda has an alkaline pH of 9. Natural precipitation typically has a pH level of about 5.2.

Scientists quickly realized that the low pH readings at Hubbard Brook warranted closer scrutiny. Past research has shown that acidic pH levels can have serious environmental consequences. In aquatic and wetland ecosystems a range of organisms, such as salamanders, rainbow trout, frogs and crayfish, die when pH levels fall below 4.5. In addition to harming wildlife, acid precipitation can impact tree vigor and growth, degrade soil quality and lower crop yields. Since the early 1960s, a team of scientists, led by Dr. Likens, has been gathering and assessing long-term data on precipitation chemistry at the Hubbard Brook Experimental Forest. Other scientists here working on the problem of acid rain and air pollution include Dr. Kathleen Weathers, Dr. Gary Lovett, Mr. Donald Buso, and Mr. Thomas Butler.

With low levels of human development and 3,160 hectares (7,200 acres) of unbroken, forested lands, to the casual observer the Hubbard Brook Experimental Forest seems removed from the human-accelerated environmental changes that plague urbanized, industrial and more developed areas. What was causing acidic precipitation to fall in an isolated New Hampshire forest? Furthermore, how could scientists prevent pH levels from rising to levels that would irreparably harm the ecosystem? The results of over forty years of careful research points to one obvious culprit- fossil fuel combustion. Minimizing acid precipitation depends upon curtailing the acid-forming pollutants.

When heating homes, utilizing electricity, or driving vehicles, most of us rely on fossil fuel energy. When combusted, fossil fuels such as coal and oil emit acid-forming nitrogen and sulfur oxides. These compounds mix in the atmosphere, often traveling thousands of kilometers from their original source. As a result, pollutants from power plants in southern New Jersey or southern Michigan can impact pristine forests in undeveloped parts of New Hampshire.

Research at the Hubbard Brook Experimental Forest has made significant inroads into understanding and controlling acid precipitation. Innovations in reducing fossil fuel emissions, such as taller stacks on factories, catalytic converters, and low-sulfur coal, all have been employed in response to results of acid deposition research. Dr. Likens' insight has informed a range of policy measures, including the 1990 Amendments to the Clean Air Act. As a result of globalization, fossil fuel combustion is increasing around the world. If the US is to serve as a model for developing nations, it is important to keep US legislation regulating fossil fuel emissions science-based and strong.

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Whatever Happened to Acid Rain?

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But the issue seems to have disappeared since that time. Is the reason for this that we actually solved a pressing environmental problem, or did acid rain simply get pushed down the priority list as new, more urgent environmental issues came to the forefront?

What is Acid Rain?     

Acid rain is rain or any other type of precipitation, including snow or fog, that is unusually acidic. Acid rain is caused by sulfur dioxide, or nitrogen dioxide emissions released into the air and react with water molecules before falling to the ground as rain or snow. Most sulfur or nitrogen dioxide comes from electrical power plants, with a smaller amount coming from cars and other vehicles and natural sources such as volcanoes and wildfires. Both emissions, move by circulating air and wind, can travel long distances so that acid rain may be found in areas far from its source.     

Acid rain can create highly acidic soils, adversely affecting the growth of forests and crops. Acidic waters can result in the death of fish and other aquatic species. Acid rain also enhances the deposition of mercury, which has adverse effects on human health. Direct impacts on human health have also been documented. A severe episode of acid fog, the Great London Smog of 1952, resulted in an increase in the daily average death rate from 252 to approximately 1,000, and acid fog was r esponsible  for several severe air pollution episodes in southern California in the 1980s. 

• 1852 - Scientists identified a relationship between acid rain and air pollution in Manchester, England.
• 1972 - Scientists discovered rain deposited in the White Mountains in New Hampshire was acidic. 
• 1980 - Congress passed the Acid Deposition Act establishing an 18-year assessment and research program on acid rain.
• 1983 - National Academy of Sciences (NAS) issues a draft report saying that acid rain is a real problem that needs to be addressed.
• 1990 - Congress passed a series of amendments to the Clean Air Act establishing a cap-and-trade system designed to control sulfur dioxide emissions. A more traditional regulatory program was established to control nitrogen dioxide emissions.

What is cap-and-trade?

“We devised a cap-and-trade approach, written into the 1990 Clean Air Act. It required cutting overall sulfur emissions in half, but let each company decide how to make the cuts. Power plants that lowered their pollution more than required could sell those extra allowances to other plants. A new commodities market was born.”

Environmental Defense Fund

Cap-and-trade is a market-based solution to environmental concerns developed with all stakeholders, the regulators, environmental advocates, and businesses. 

• EPA sets a cap, or a limit, on the total amount of sulfur dioxide allowed to be emitted by all electric-generating power plants in the U.S.
• Allowances are “authorizations to emit” allocated to every power plant.   
• An allowance market was set up that allows power plants and others to buy or sell allowances throughout the year.
• Power plants are given the flexibility to choose their own options to reduce emissions, such as adding emission controls, using more advanced technologies, switching to new fuels, using banked allowances, or buying allowances from the market.   
• At the end of every compliance period, each power plant must have enough allowances to cover their sulfur dioxide emissions, or the EPA fines them.

This system gives businesses strong financial incentives to cut emissions. Electrical power plants emitted 778 thousand tons of sulfur dioxide in 2020 , well below  the permanent cap of 8.95 million tons.

What Happened?

A 93% reduction in annual sulfur dioxide emissions between 1990 and 2019! 

There was also an 87% reduction in annual nitrogen dioxide emissions between 1990 and 2019. 

Significant decreases occurred in acid rain nationwide – wet sulfate deposition, an indicator of acid rain, decreased by 68% between 1989 and 2019.   

Why Such Little Attention?

The acid rain issue has been called “the greatest green success story of the past decade” by  The Economist  in their article “The Invisible Green Hand.” Two factors may explain why we heard so much about acid rains' harmful effects and so little about our successful mitigation. First, economic solutions often become baked in, integrated into our economy, creating an invisible fix not apparent to most people. Second, journalists just don’t like to cover good news stores – it doesn’t gather our attention and emotional responses the way bad news does. 

Conclusions

The acid rain story should be studied by every person interested in environmental policy. The cap-and-trade approach is currently being used to help solve climate change in the U.S. and globally.  For example , California instituted a cap-and-trade policy for carbon emissions, leading to a steady decline in carbon dioxide emissions. The European Union capped carbon dioxide emissions from some industrial sources, which led to a 29% reduction from 2005 to 2018. China, the world’s largest emitter of greenhouse gases, began a carbon cap-and-trade program in 2017. 

On a broader level, acid rain should give us hope for the future that the government, private sector, and non-profits, working with technological solutions, can solve today’s pressing problems. Acid rain was an issue that seemed unsolvable 40 years ago, but today is held up as an example as to what is achievable.   

[1] The EPA’s  website , from which the graphic was taken, has several interactive charts showing the significant improvement in our air over the last 30 years. 

Sources:  Environmental Defense Fund.  How Cap and Trade Works  ,   How Economics solved acid rain

U.S. Environmental Protection Agency:  Acid Rain Program ,  Acid Rain Program Results

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acid rain , precipitation possessing a pH of about 5.2 or below primarily produced from the emission of sulfur dioxide (SO 2 ) and nitrogen oxides (NO x ; the combination of NO and NO 2 ) from human activities, mostly the combustion of fossil fuels . In acid-sensitive landscapes, acid deposition can reduce the pH of surface waters and lower biodiversity . It weakens trees and increases their susceptibility to damage from other stressors, such as drought , extreme cold, and pests . In acid-sensitive areas, acid rain also depletes soil of important plant nutrients and buffers, such as calcium and magnesium , and can release aluminum , bound to soil particles and rock , in its toxic dissolved form. Acid rain contributes to the corrosion of surfaces exposed to air pollution and is responsible for the deterioration of limestone and marble buildings and monuments.

The phrase acid rain was first used in 1852 by Scottish chemist Robert Angus Smith during his investigation of rainwater chemistry near industrial cities in England and Scotland . The phenomenon became an important part of his book Air and Rain: The Beginnings of a Chemical Climatology (1872). It was not until the late 1960s and early 1970s, however, that acid rain was recognized as a regional environmental issue affecting large areas of western Europe and eastern North America . Acid rain also occurs in Asia and parts of Africa , South America , and Australia . As a global environmental issue, it is frequently overshadowed by climate change . Although the problem of acid rain has been significantly reduced in some areas, it remains an important environmental issue within and downwind from major industrial and industrial agricultural regions worldwide .

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Depending on where you live, maybe you've heard of acid rain. Now, acid rain is not pure acid falling from the sky, but rather it is rainfall or atmospheric moisture that has been mixed with elements and gases that have caused the moisture to become more acidic than normal. Pure water has a pH of 7, and, generally, rainfall is somewhat on the acidic side (a bit less than 6). But, acid rain can have a pH of about 5.0-5.5, and can even be in the 4 range in the northeastern United States, where there are a lot of industries and cars.

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Causes of acid rain

Acidic precipitation can be caused by natural (volcanoes) and man-made activities, such as from cars and in the generation of electricity. The precursors, or chemical forerunners, of acid rain formation result from both natural sources, such as volcanoes and decaying vegetation, and man-made sources, primarily emissions of sulfur dioxide (SO 2 ) and nitrogen oxides (NO x ) resulting from fossil fuel combustion. The burning of fossil fuels (coal and oil) by power-production companies and industries releases sulfur into the air that combines with oxygen to form sulfur dioxide (SO 2 ). Exhausts from cars cause the formation of nitrogen oxides in the air. From these gases, airborne sulfuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ) can be formed and be dissolved in the water vapor in the air. Although acid-rain gases may originate in urban areas, they are often carried for hundreds of miles in the atmosphere by winds into rural areas. That is why forests and lakes in the countryside can be harmed by acid rain that originates in cities.

Effects of acid rain

The environment can generally adapt to a certain amount of acid rain. Often soil is slightly basic (due to naturally occurring limestone, which has a pH of greater than 7). Because bases counteract acids, these soils tend to balance out some of the acid rain's acidity. But in areas, such as some of the Rocky Mountains and parts of the northwestern and southeastern United States, where limestone does not naturally occur in the soil, acid rain can harm the environment.

Some fish and animals, such as frogs, have a hard time adapting to and reproducing in an acidic environment. Many plants, such as evergreen trees, are damaged by acid rain and acid fog. I've seen some of the acid-rain damage to the evergreen forests in the Black Forest of Germany. Much of the Black Forest was indeed black because so much of the green pine needles had been destroyed, leaving only the black trunks and limbs! You also might notice how acid rain has eaten away the stone in some cities' buildings and stone artwork.

Geographic distribution of acid rain

Acidity in rain is measured by collecting samples of rain and measuring its pH. To find the distribution of rain acidity, weather conditions are monitored and rain samples are collected at sites all over the country. The areas of greatest acidity (lowest pH values) are located in the Northeastern United States. This pattern of high acidity is caused by the large number of cities, the dense population, and the concentration of power and industrial plants in the Northeast. In addition, the prevailing wind direction brings storms and pollution to the Northeast from the Midwest, and dust from the soil and rocks in the Northeastern United States is less likely to neutralize acidity in the rain.

Acid rain and stone

When you hear or read in the media about the effects of acid rain, you are usually told about the lakes, fish, and trees in New England and Canada. However, we are becoming aware of an additional concern: many of our historic buildings and monuments are located in the areas of highest acidity. In Europe, where buildings are much older and pollution levels have been ten times greater than in the United States, there is a growing awareness that pollution and acid rain are accelerating the deterioration of buildings and monuments.

Stone weathers (deteriorates) as part of the normal geologic cycle through natural chemical, physical, and biological processes when it is exposed to the environment. This weathering process, over hundreds of millions of years, turned the Appalachian Mountains from towering peaks as high as the Rockies to the rounded knobs we see today. Our concern is that air pollution, particularly in urban areas, may be accelerating the normal, natural rate of stone deterioration, so that we may prematurely lose buildings and sculptures of historic or cultural value.

What about buildings?

Many buildings and monuments are made of stone, and many buildings use stone for decorative trim. Granite is now the most widely used stone for buildings, monuments, and bridges. Limestone is the second most used building stone. It was widely used before Portland cement became available in the early 19th century because of its uniform color and texture and because it could be easily carved. Sandstone from local sources was commonly used in the Northeastern United States, especially before 1900. Nationwide, marble is used much less often than the other stone types, but it has been used for many buildings and monuments of historical significance. Because of their composition, some stones are more likely to be damaged by acidic deposition than others. Granite is primarily composed of silicate minerals, like feldspar and quartz, which are resistant to acid attack. Sandstone is also primarily composed of silica and is thus resistant. A few sandstones are less resistant because they contain a carbonate cement that dissolves readily in weak acid. Limestone and marble are primarily composed of the mineral calcite (calcium carbonate), which dissolves readily in weak acid; in fact, this characteristic is often used to identify the mineral calcite.

How does acid precipitation affect marble and limestone buildings?

Acid precipitation affects stone primarily in two ways: dissolution and alteration. When sulfurous, sulfuric, and nitric acids in polluted air react with the calcite in marble and limestone, the calcite dissolves. In exposed areas of buildings and statues, we see roughened surfaces, removal of material, and loss of carved details. Stone surface material may be lost all over or only in spots that are more reactive.

You might expect that sheltered areas of stone buildings and monuments would not be affected by acid precipitation. However, sheltered areas on limestone and marble buildings and monuments show blackened crusts that have spalled (peeled) off in some places, revealing crumbling stone beneath. This black crust is primarily composed of gypsum, a mineral that forms from the reaction between calcite, water, and sulfuric acid. Gypsum is soluble in water ; although it can form anywhere on carbonate stone surfaces that are exposed to sulfur dioxide gas (SO 2 ), it is usually washed away. It remains only on protected surfaces that are not directly washed by the rain. Gypsum is white, but the crystals form networks that trap particles of dirt and pollutants, so the crust looks black. Eventually the black crusts blister and spall off, revealing crumbling stone.

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The erosion of carbonate stone by acid rain: laboratory and field investigations, [book review] the acid rain controversy, by j. l. regens and r. w. rycroft, the effects of air pollution and acid rain on fish, wildlife, and their habitats-urban ecosystems, the effects of air pollution and acid rain on fish, wildlife, and their habitats-rivers and streams, the effects of air pollution and acid rain on fish, wildlife, and their habitats-lakes, the effects of air pollution and acid rain on fish, wildlife, and their habitats-introduction, the effects of air pollution and acid rain on fish, wildlife, and their habitats-forests.

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How aquatic environments respond to acid deposition depends on their sensitivity to acids and the quantity of acids received. Most environments are naturally buffered against acid input by neutralizing materials such as limestone. If sufficient buffering capacity exists in an environment, excessive acid input does not change the pH of the water, although it will progressively deplete its acid neutralizing capacity (ANC). The soils, bedrock, and vegetation of watersheds largely determine the capacity of aquatic resources to accommodate acid deposition, but other factors play an important role. Acid neutralizing capacity can have its full effect only when the incoming precipitation has sufficient contact time with the neutralizing material. Areas with steep slopes, shallow soils or frozen ground tend to minimize contact time, resulting in incomplete neutralization of water entering lakes and streams. Additional neutralization is provided by the biota. For example, algae generate buffering materials during photosynthesis, and microbes living in bottom sediments reduce sulfur compounds to inert forms.ANC and pH interact in an unusual way: as acid is added to a buffered system, pH changes little until the ANC approaches zero. Then, small additions of acid cause large changes in pH. Finally, pH drops precipitously and permanently to levels that few aquatic organisms can tolerate. With lower pH, levels of toxic metals leached from the watershed increase, aquatic growth is reduced, and sensitive species ranging from fish to algae disappear. If this occurs in a drinking water supply, metals will dissolve from distribution pipes resulting in high levels of iron, copper, lead and other metals.

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Research progress of tio 2 modification and photodegradation of organic pollutants.

Graphical Abstract

1. Introduction

2. mechanism and kinetics of photodegradation of organic pollutants by tio 2 photocatalyst, 2.1. mechanism of photodegradation of organic pollutants by tio 2 photocatalyst, 2.2. kinetics of photodegradation of organic pollutants by tio 2 photocatalyst.

• Solution pH value has an important effect on photocatalytic degradation. The photocatalytic activity of TiO 2 may vary under acidic and alkaline conditions.
• The amount of catalyst dosing will also affect the degradation rate. Less than or more than the optimal dosage will lead to a decrease in the degradation rate.
• Factors such as organic pollutant’s initial concentration and light intensity also affect the kinetic process of photocatalytic degradation.

3. Synthesis Method of TiO 2 Photocatalyst

3.1. sol-gel method, 3.2. hydrothermal synthesis, 3.3. atomic layer deposition method, 3.4. microemulsion method, 3.5. other synthesis methods, 4. modification method of tio 2 photocatalyst, 4.1. precious metal-doped titanium dioxide, 4.2. transition metal-doped titanium dioxide, 4.2.1. doping with a single transition metal elements, 4.2.2. co-doping of transition metal elements, 4.3. rare earth metal-doped titanium dioxide, 4.3.1. doping with a single rare earth metal element, 4.3.2. co-doping with rare earth metal elements, 4.3.3. co-doping of rare earth elements with other elements, 4.4. compound semiconductors based on titanium dioxide.

• By manipulating the size of the modified particles, the spectral absorption range and bandgap of the semiconductor material can be effectively tuned utilizing the quantum size effect [ 107 , 108 ].
• Surface modification of TiO 2 plays a role in improving the photostability of the semiconductor materials [ 109 ].
• Given that light absorption in semiconductors mainly occurs at the band-edge, the semiconductor composite facilitates more efficient harvesting of sunlight [ 110 ].

Click here to enlarge figure

4.4.1. Titanium Dioxide Composites with Common Semiconductors

4.4.2. titanium dioxide hybrid materials with graphene, 4.5. tio 2 composite polymers, 5. summary and outlook, 5.1. summary of research progress.

• By doping precious metals, transition metals, rare earth metals, or non-metallic elements, TiO 2 can change the band structure, broaden its light absorption range, and improve the separation efficiency of photoelectron-hole pairs, which can significantly improve the photocatalytic activity of TiO 2 .
• TiO 2 was mixed with other semiconductor materials to form a composite photocatalytic material with a heterogeneous structure. This modification method can make use of the synergistic effect between different materials to improve the utilization efficiency of photogenerated electron-hole pairs and enhance photocatalytic performance. For example, the composite of TiO 2 with SiO 2 , ZnO, and other materials can form heterogeneous structures and improve photocatalytic efficiency.
• By introducing functional material polymer on the surface of TiO 2 , the surface properties of TiO 2 are improved, and the photocatalytic performance is improved. Surface modification can increase the active sites on the surface of TiO 2 and promote the separation and migration of photogenerated electrons and holes.

5.2. Future Research Direction and Development Trend

Author contributions, data availability statement, conflicts of interest.

• Song, Y.; Wang, L.; Qiang, X.; Gu, W.; Ma, Z.; Wang, G. An Overview of Biological Mechanisms and Strategies for Treating Wastewater from Printing and Dyeing Processes. J. Water Process Eng. 2023 , 55 , 104242. [ Google Scholar ] [ CrossRef ]
• Ewuzie, U.; Saliu, O.D.; Dulta, K.; Ogunniyi, S.; Bajeh, A.O.; Iwuozor, K.O.; Ighalo, J.O. A Review on Treatment Technologies for Printing and Dyeing Wastewater (PDW). J. Water Process Eng. 2022 , 50 , 103273. [ Google Scholar ] [ CrossRef ]
• Dong, H.; Guo, T.; Zhang, W.; Ying, H.; Wang, P.; Wang, Y.; Chen, Y. Biochemical Characterization of A Novel Azoreductase from Streptomyces sp.: Application in Eco-Friendly Decolorization of Azo Dye Wastewater. Int. J. Biol. Macromol. 2019 , 140 , 1037–1046. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Hu, Z.; Guan, D.; Sun, Z.; Zhang, Z.; Shan, Y.; Wu, Y.; Gong, C.; Ren, X. Osmotic Cleaning of Typical Inorganic and Organic Foulants on Reverse Osmosis Membrane for Textile Printing and Dyeing Wastewater Treatment. Chemosphere 2023 , 336 , 139162. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Jing, X.; Yuan, J.; Cai, D.; Li, B.; Hu, D.; Li, J. Concentrating And Recycling of High-Concentration Printing and Dyeing Wastewater by A Disc Tube Reverse Osmosis-Fenton Oxidation/Low-Temperature Crystallization Process. Sep. Purif. Technol. 2021 , 266 , 118583. [ Google Scholar ] [ CrossRef ]
• Deng, D.; Lamssali, M.; Aryal, N.; Ofori-Boadu, A.; Jha, M.K.; Samuel, R.E. Textiles Wastewater Treatment Technology: A Review. Water Environ. Res. Res. Publ. Water Environ. Fed. 2020 , 92 , 1805–1810. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Katheresan, V.; Kansedo, J.; Lau, S.Y. Efficiency of Various Recent Wastewater Dye Removal Methods: A Review. J. Environ. Chem. Eng. 2018 , 6 , 4676–4697. [ Google Scholar ] [ CrossRef ]
• Li, W.; Mu, B.; Yang, Y. Feasibility Of Industrial-Scale Treatment of Dye Wastewater Via Bio-Adsorption Technology. Bioresour. Technol. 2019 , 277 , 157–170. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Zhao, L.; Huang, L.; Zheng, Z.; Wei, J.; Qiu, Z.; Zeng, D. Enhanced Degradation Performance of Fe(75)B(12.5)Si(12.5) Amorphous Alloys On Azo Dye. Environ. Sci. Pollut. Res. Int. 2023 , 30 , 34428–34439. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• González-Martínez, S.; Piña-Mondragón, S.; González-Barceló, Ó. Treatment of The Azo Dye Direct Blue 2 in A Biological Aerated Filter under Anaerobic/Aerobic Conditions. Water Sci. Technol. J. Int. Assoc. Water Pollut. Res. 2010 , 61 , 789–796. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Araújo, S.; Damianovic, M.; Foresti, E.; Florencio, L.; Kato, M.T.; Gavazza, S. Biological Treatment of Real Textile Wastewater Containing Sulphate, Salinity, and Surfactant Through An Anaerobic-Aerobic System. Water Sci. Technol. J. Int. Assoc. Water Pollut. Res. 2022 , 85 , 2882–2898. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Liu, X.; Chen, Z.; Du, W.; Liu, P.; Zhang, L.; Shi, F. Treatment of Wastewater Containing Methyl Orange Dye By Fluidized Three Dimensional Electrochemical Oxidation Process Integrated with Chemical Oxidation And Adsorption. J. Environ. Manag. 2022 , 311 , 114775. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Ramalingam, G.; Perumal, N.; Priya, A.K.; Rajendran, S. A Review of Graphene-Based Semiconductors for Photocatalytic Degradation of Pollutants in Wastewater. Chemosphere 2022 , 300 , 134391. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Silva, T.E.M.; Moreira, A.J.; Nobrega, E.T.D.; Alencar, R.G.; Rabello, P.T.; Blaskievicz, S.F.; Marques, G.N.; Mascaro, L.H.; Paris, E.C.; Lemos, S.G.; et al. Hierarchical Structure of 3D Zno Experimentally Designed to Achieve High Performance in The Sertraline Photocatalysis in Natural Waters. Chem. Eng. J. 2023 , 475 , 146235. [ Google Scholar ] [ CrossRef ]
• Syahidatul Insyirah Mohd Foad, N.; Abu Bakar, F. Synthesis of TiO 2 Photocatalyst with Tunable Optical Properties and Exposed Facet for Textile Wastewater Treatment. Results Opt. 2023 , 13 , 100545. [ Google Scholar ]
• Thuan, D.V.; Chu, T.T.H.; Thanh, H.D.T.; Le, M.V.; Ngo, H.L.; Le, C.L.; Thi, H.P. Adsorption and Photodegradation of Micropollutant in Wastewater by Photocatalyst TiO 2 /Rice Husk Biochar. Environ. Res. 2023 , 236 , 116789. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Santhosh, A.M.; Yogendra, K.; Madhusudhana, N.; Mahadevan, K.M.; Veena, S.R. Efficient Photodegradation of Victoria Blue B and Acridine Orange Dyes by Nickel Oxide Nanoparticles. Mater. Today Proc. 2023 , 92 , 1616–1622. [ Google Scholar ] [ CrossRef ]
• Chen, D.; Cheng, Y.; Zhou, N.; Chen, P.; Wang, Y.; Li, K.; Huo, S.; Cheng, P.; Peng, P.; Zhang, R.; et al. Photocatalytic Degradation of Organic Pollutants Using TiO 2 -Based Photocatalysts. J. Clean. Prod. 2020 , 268 , 121725. [ Google Scholar ] [ CrossRef ]
• Saeed, M.; Muneer, M.; Haq, A.U.; Akram, N. Photocatalysis: An Effective Tool for Photodegradation of Dyes—A Review. Environ. Sci. Pollut. Res. 2022 , 29 , 293–311. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Ul Haq, I.; Ahmad, W.; Ahmad, I.; Yaseen, M. Photocatalytic Oxidative Degradation of Hydrocarbon Pollutants In Refinery Wastewater Using TiO 2 As Catalyst. Water Environ. Res. Res. Publ. Water Environ. Fed. 2020 , 92 , 2086–2094. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Armaković, S.J.; Savanović, M.M.; Šiljegović, M.V.; Kisić, M.; Šćepanović, M.; Grujić-Brojčin, M.; Simić, N.; Gavanski, L.; Armaković, S. Self-Cleaning and Charge Transport Properties of Foils Coated with Acrylic Paint Containing TiO 2 Nanoparticles. Inorganics 2024 , 12 , 35. [ Google Scholar ] [ CrossRef ]
• Ravelli, D.; Dondi, D.; Fagnoni, M.; Albini, A. Titanium Dioxide Photocatalysis: An Assessment of The Environmental Compatibility for The Case of The Functionalization of Heterocyclics. Appl. Catal. B Environ. 2010 , 99 , 442–447. [ Google Scholar ] [ CrossRef ]
• Li, M.; Liu, H.; Song, Y.; Li, Z. TiO 2 Homojunction with Au Nanoparticles Decorating as An Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction. Mater. Charact. 2019 , 151 , 286–291. [ Google Scholar ] [ CrossRef ]
• El Mragui, A.; Zegaoui, O.; Daou, I. Synthesis, Characterization and Photocatalytic Properties under Visible Light of Doped and Co-Doped TiO 2 -Based Nanoparticles. Mater. Today Proc. 2019 , 13 , 857–865. [ Google Scholar ] [ CrossRef ]
• El-Kholy, R.A.; Isawi, H.; Zaghlool, E.; Soliman, E.A.; Khalil, M.M.H.; Said, M.M.; El-Aassar, A.M. Preparation and Characterization of Rare Earth Element Nanoparticles for Enhanced Photocatalytic Degradation. Environ. Sci. Pollut. Res. Int. 2023 , 30 , 69514–69532. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Kumar, S.G.; Rao, K.S.R.K. Comparison Of Modification Strategies towards Enhanced Charge Carrier Separation and Photocatalytic Degradation Activity of Metal Oxide Semiconductors (TiO 2 , WO 3 And Zno). Appl. Surf. Sci. 2017 , 391 , 124–148. [ Google Scholar ] [ CrossRef ]
• Srinithi, S.; Balakumar, V.; Chen, T.-W.; Chen, S.-M.; Akilarasan, M.; Lou, B.-S.; Yu, J. In-Situ Fabrication of TiO 2 -MWCNT Composite for An Efficient Electron Transfer Photocatalytic Rhodamine B Dye Degradation under UV–Visible Light. Diam. Relat. Mater. 2023 , 138 , 110245. [ Google Scholar ] [ CrossRef ]
• Makota, O.; Dutková, E.; Briančin, J.; Bednarcik, J.; Lisnichuk, M.; Yevchuk, I.; Melnyk, I. Advanced Photodegradation of Azo Dye Methyl Orange Using H 2 O 2 -Activated Fe 3 O 4 @SiO 2 @ZnO Composite under UV Treatment. Molecules 2024 , 29 , 1190. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Rubesh Ashok Kumar, S.; Vasvini Mary, D.; Suganya Josephine, G.A. Design of solar-light-driven agglomerated cluster-like transition/rare-earth metal oxide-supported carbon-based nanomaterial for the degradation of azo dye. Chem. Phys. Impact 2024 , 8 , 100563. [ Google Scholar ]
• Kumar, S.R.A.; Mary, D.V.; Josephine, G.A.S.; Sivasamy, A. Hydrothermally synthesized WO 3 :CeO 2 supported gC 3 N 4 nanolayers for rapid photocatalytic degradation of azo dye under natural sunlight. Inorg. Chem. Commun. 2024 , 164 , 112366. [ Google Scholar ] [ CrossRef ]
• Luo, L.; Shen, J.; Jin, B. Construction of Zn 0.5 Cd 0.5 S/Bi 4 O 5 Br 2 Heterojunction for Enhanced Photocatalytic Degradation of Tetracycline Hydrochloride. Inorganics 2024 , 12 , 127. [ Google Scholar ] [ CrossRef ]
• Nawaz, R.; Hanafiah, M.M.; Ali, M.; Anjum, M.; Baki, Z.A.; Mekkey, S.D.; Ullah, S.; Khurshid, S.; Ullah, H.; Arshad, U. Review of the performance and energy requirements of metals modified TiO 2 materials based photocatalysis for phenolic compounds degradation: A case of agro-industrial effluent. J. Environ. Chem. Eng. 2024 , 12 , 112766. [ Google Scholar ] [ CrossRef ]
• Zhao, H.; Dong, J.; Xie, Y.; Meng, L.; Shen, S.; Chen, J.G.; Hu, D.; Yang, G. Construction of thin-shell TiO 2 vesicles inspired by the shell-deposition of diatoms for chlorophyll-sensitized photocatalyst. Solid State Sci. 2024 , 152 , 107520. [ Google Scholar ] [ CrossRef ]
• Eddy, D.R.; Permana, M.D.; Sakti, L.K.; Sheha, G.A.N.; Solihudin; Hidayat, S.; Takei, T.; Kumada, N.; Rahayu, I. Heterophase Polymorph of TiO 2 (Anatase, Rutile, Brookite, TiO 2 (B)) for Efficient Photocatalyst: Fabrication and Activity. Nanomaterials 2023 , 13 , 704. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Razdan, N.K.; Bhan, A. Catalytic site ensembles: A context to reexamine the Langmuir-Hinshelwood kinetic description. J. Catal. 2021 , 404 , 726–744. [ Google Scholar ] [ CrossRef ]
• Arikal, D.; Kallingal, A. Photocatalytic degradation of azo and anthraquinone dye using TiO 2 /MgO nanocomposite immobilized chitosan hydrogels. Environ. Technol. 2021 , 42 , 2278–2291. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Zhang, W.; Tian, Y.; He, H.; Xu, L.; Li, W.; Zhao, D. Recent advances in the synthesis of hierarchically mesoporous TiO 2 materials for energy and environmental applications. Natl. Sci. Rev. 2020 , 7 , 1702–1725. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Naas, L.A.; Bouaouina, B.; Bensouici, F.; Mokeddem, K.; Abaidia, S.E. Effect of TiN thin films deposited by oblique angle sputter deposition on sol-gel coated TiO 2 layers for photocatalytic applications. Thin Solid Film. 2024 , 793 , 140275. [ Google Scholar ] [ CrossRef ]
• Jamil, A.; Sawaira, T.; Ali, A. Ce-TiO 2 nanoparticles with surface-confined Ce 3+ /Ce 4+ redox pairs for rapid sunlight-driven elimination of organic contaminants from water. Environ. Nanotechnol. Monit. Manag. 2024 , 21 , 100946. [ Google Scholar ] [ CrossRef ]
• Huo, J.; Xiao, Y.; Yang, H. Ultrasmall TiO 2 /C nanoparticles with oxygen vacancy-enriched as an anode material for advanced Li-ion hybrid capacitors. J. Energy Storage 2024 , 89 , 111586. [ Google Scholar ] [ CrossRef ]
• Fermeli, P.N.; Lagopati, N.; Gatou, A.M. Biocompatible PANI-Encapsulated Chemically Modified Nano-TiO 2 Particles for Visible-Light Photocatalytic Applications. Nanomaterials 2024 , 14 , 642. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Parashar, D.; Achari, G.; Kumar, M. Multi-antibiotics removal under UV-A light using sol-gel prepared TiO 2 : Central composite design, effect of persulfate addition and degradation pathway study. Chemosphere 2023 , 341 , 140025. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Gnanasekaran, L.; Priya, A.K.; Ghfar, A.A.; Sekar, K.; Santhamoorthy, M.; Arthi, M.; Soto-Moscoso, M. The influence of heterostructured TiO 2 /ZnO nanomaterials for the removal of azo dye pollutant. Chemosphere 2022 , 308 , 136161. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Ioannidou, T.; Anagnostopoulou, M.; Vasiliadou, I.A.; Marchal, C.; Alexandridou, E.O.; Keller, V.; Christoforidis, K.C. Mixed phase anatase nanosheets/brookite nanorods TiO 2 photocatalysts for enhanced gas phase CO 2 photoreduction and H 2 production. J. Environ. Chem. Eng. 2024 , 12 , 111644. [ Google Scholar ] [ CrossRef ]
• Rawat, J.; Sharma, H.; Dwivedi, C. Microwave-assisted synthesis of carbon quantum dots and their integration with TiO 2 nanotubes for enhanced photocatalytic degradation. Diam. Relat. Mater. 2024 , 144 , 111050. [ Google Scholar ] [ CrossRef ]
• Matakgane, M.; Mokoena, T.; Kroon, R. Robust upconversion luminescence of Ho 3+ /Yb 3+ co-doped TiO 2 nanophosphors manifested by crystallinity. J. Mol. Struct. 2024 , 1305 , 137747. [ Google Scholar ] [ CrossRef ]
• Yang, W.; Jia, N.; Xu, W.; Bu, Q. Fabrication of novel 3D urchin-like mixed-phase TiO 2 for efficient degradation of trimethoprim. Mater. Lett. 2023 , 351 , 135001. [ Google Scholar ] [ CrossRef ]
• Zhang, W.; Zhao, X.; Zhang, L.; Zhu, J.; Li, S.; Hu, P.; Feng, J.; Yan, W. Insight into the effect of surface carboxyl and amino groups on the adsorption of titanium dioxide for acid red G. Front. Chem. Sci. Eng. 2021 , 15 , 1147–1157. [ Google Scholar ] [ CrossRef ]
• Jialin, L.; Zhonghao, W.; Furui, C. Self-assembly, structure and catalytic activity of Ni 3 on TiO 2 : A triple-atom catalyst for hydrogen evolution. Appl. Surf. Sci. 2024 , 643 , 158719. [ Google Scholar ]
• Abidi, M.; Assadi, A.; Bouzaza, A. Photocatalytic indoor/outdoor air treatment and bacterial inactivation on CuO/TiO 2 prepared by HiPIMS on polyester cloth under low intensity visible light. Appl. Catal. B Environ. 2019 , 259 , 118074. [ Google Scholar ] [ CrossRef ]
• Cao, Y.-Q.; Zi, T.-Q.; Zhao, X.-R.; Liu, C.; Ren, Q.; Fang, J.-B.; Li, W.-M.; Li, A.-D. Enhanced visible light photocatalytic activity of Fe2O3 modified TiO2 prepared by atomic layer deposition. Sci. Rep. 2020 , 10 , 13437. [ Google Scholar ] [ CrossRef ]
• Feng, J.; Xiong, S.; Ren, L.; Wang, Y. Atomic layer deposition of TiO 2 on carbon-nanotubes membrane for capacitive deionization removal of chromium from water. Chin. J. Chem. Eng. 2022 , 45 , 15–21. [ Google Scholar ] [ CrossRef ]
• Ostyn, N.R.; Sree, S.P.; Li, J.; Feng, J.Y.; Roeffaers, M.B.; De Feyter, S.; Dendooven, J.; Detavernier, C.; Martens, J.A. Covalent graphite modification by low-temperature photocatalytic oxidation using a titanium dioxide thin film prepared by atomic layer deposition. Catal. Sci. Technol. 2021 , 11 , 6724–6731. [ Google Scholar ] [ CrossRef ]
• Ke, W.; Qin, X.; Vazquez, Y.; Lee, I.; Zaera, F. Direct characterization of interface sites in Au/TiO 2 catalysts prepared using atomic layer deposition. Chem Catal. 2024 , 4 , 100977. [ Google Scholar ] [ CrossRef ]
• Lys, A.; Gnilitskyi, I.; Coy, E.; Jancelewicz, M.; Gogotsi, O.; Iatsunskyi, I. Highly regular laser-induced periodic silicon surface modified by MXene and ALD TiO 2 for organic pollutants degradation. Appl. Surf. Sci. 2023 , 640 , 15833. [ Google Scholar ] [ CrossRef ]
• Domenico, R.; Francesca, D.A.; Irene, B.; Paola, B.M.; Luca, D.P. Easy way to produce iron-doped titania nanoparticles via the solid-state method and investigation their photocatalytic activity. J. Mater. Res. 2023 , 38 , 1282–1292. [ Google Scholar ]
• Sun, L.; Zhou, Q.; Mao, J.; Ouyang, X.; Yuan, Z.; Song, X.; Gong, W.; Mei, S.; Xu, W. Study on Photocatalytic Degradation of Acid Red 73 by Fe 3 O 4 @TiO 2 Exposed (001) Facets. Appl. Sci. 2022 , 12 , 3574. [ Google Scholar ] [ CrossRef ]
• Yang, J.X.; Chang, W.; Huang, L.; Qin, J.; Li, Y.F. Preparation and properties of titanium dioxide nanofibers by microemulsion electrospinning. Chem. Ind. Eng. 2022 , 39 , 21–28. [ Google Scholar ]
• Sun, L.; Wang, G.; Bi, S.; Li, H.; Zhan, H.; Liu, W. Synergistic modulation of oxygen vacancies and heterojunction structure in Pd@CN@TiO 2 promotes efficient photocatalytic Suzuki–Miyaura C–C coupling reactions. J. Appl. Organomet. Chem. 2024 , 38 , e7353. [ Google Scholar ] [ CrossRef ]
• Hongying, L.; Bicheng, Z.; Jian, S.; Haiming, G.; Jiaguo, Y.; Liuyang, Z. Photocatalytic hydrogen production from seawater by TiO 2 /RuO 2 hybrid nanofiber with enhanced light absorption. J. Colloid Interface Sci. 2024 , 654 , 1010–1019. [ Google Scholar ]
• Andrea, B.S.; Roberto, F.; Armeli, I.M.T.; Javier, L.-T.F.; José, U.F.; Salvatore, S. H2 production through glycerol photoreforming using one-pot prepared TiO 2 -rGO-Au photocatalysts. Mol. Catal. 2023 , 547 , 113346. [ Google Scholar ]
• Djeda, R.; Mailhot, G.; Prevot, V. Porous Layered Double Hydroxide/TiO 2 Photocatalysts for the Photocatalytic Degradation of Orange II. ChemEngineering 2020 , 4 , 39. [ Google Scholar ] [ CrossRef ]
• Zhao, Y.; Ge, H.; Kondo, Y.; Kuwahara, Y.; Mori, K.; Yamashita, H. Photosynthesis of hydrogen peroxide in a two-phase system by hydrophobic Au nanoparticle-deposited plasmonic TiO 2 catalysts. Catal. Today 2024 , 431 , 114558. [ Google Scholar ] [ CrossRef ]
• Li, S.; Hu, M.; Chen, X.; Sui, S.; Jin, L.; Geng, Y.; Jiang, J.; Liu, A. The Performance And Functionalization of Modified Cementitious Materials Via Nano Titanium-Dioxide: A Review. Case Stud. Constr. Mater. 2023 , 19 , E02414. [ Google Scholar ] [ CrossRef ]
• Khitous, A.; Noel, L.; Molinaro, C.; Vidal, L.; Grée, S.; Soppera, O. Sol-Gel TiO 2 Thin Film on Au Nanoparticles for Heterogeneous Plasmonic Photocatalysis. ACS Appl. Mater. Interfaces 2024 , 16 , 10856–10866. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Chen, J.; Qiu, F.; Xu, W.; Cao, S.; Zhu, H. Recent Progress In Enhancing Photocatalytic Efficiency of TiO 2 -Based Materials. Appl. Catal. A-Gen. 2015 , 495 , 131–140. [ Google Scholar ] [ CrossRef ]
• Hou, W.; Hung, W.H.; Pavaskar, P.; Goeppert, A.; Aykol, M.; Cronin, S.B.J.A.C. Photocatalytic Conversion of CO 2 to Hydrocarbon Fuels Via Plasmon-Enhanced Absorption and Metallic Interband Transitions. ACS Catal. 2011 , 1 , 929–936. [ Google Scholar ] [ CrossRef ]
• Bhatti, M.A.; Shah, A.A.; Almaani, K.F.; Tahira, A.; Chandio, A.D.; Willander, M.; Nur, O.; Mugheri, A.Q.; Bhatti, A.L.; Waryani, B.; et al. TiO 2 /ZnO Nanocomposite Material For Efficient Degradation Of Methylene Blue. J. Nanosci. Nanotechnol. 2021 , 21 , 2511–2519. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Chacon-Argaez, U.; Cedeño-Caero, L.; Cadena-Nava, R.D.; Ramirez-Acosta, K.; Moyado, S.F.; Sánchez-López, P.; Alonso Núñez, G. Photocatalytic Activity and Biocide Properties of Ag-TiO 2 Composites on Cotton Fabrics. Materials 2023 , 16 , 4513. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Borrego PÉRez, J.A.; Morales, E.R.; Paraguay Delgado, F.; Meza Avendaño, C.A.; Alonso Guzman, E.M.; Mathews, N.R. Ag Nanoparticle Dispersed TiO 2 Thin Films by Single Step Sol-Gel Process: Evaluation of The Physical Properties and Photocatalytic Degradation. Vacuum 2023 , 215 , 112276. [ Google Scholar ] [ CrossRef ]
• Majeed, A.; Ibrahim, A.H.; Al-Rawi, S.S.; Iqbal, M.A.; Kashif, M.; Yousif, M.; Abidin, Z.U.; Ali, S.; Arbaz, M.; Hussain, S.A. Green Organo-Photooxidative Method for the Degradation of Methylene Blue Dye. ACS Omega 2024 , 9 , 12069–12083. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Wang, Z.; Jin, X.; Chen, F.; Kuang, X.; Min, J.; Duan, H.; Li, J.; Chen, J. Oxygen Vacancy Induced Interaction between Pt and TiO 2 to Improve The Oxygen Reduction Performance. J. Colloid Interface Sci. 2023 , 650 , 901–912. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Liu, L.; He, A. Optical And Electrochemical Study On The Performance Of Au@ TiO 2 Core-Shell Heterostructured Nanoparticles as Photocatalyst for Photodegradation of Methylene Blue under Solar-Light Irradiation. Int. J. Electrochem. Sci. 2022 , 17 , 220636. [ Google Scholar ] [ CrossRef ]
• Zuo, J.; Ma, X.; Tan, C.; Xia, Z.; Zhang, Y.; Yu, S.; Li, Y.; Li, Y.; Li, J. Preparation of Au-RGO/TiO 2 Nanotubes and Study on The Photocatalytic Degradation of Ciprofloxacin. Anal. Methods Adv. Methods Appl. 2023 , 15 , 519–528. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Zheng, F.; Martins, P.M.; Queirós, J.M.; Tavares, C.J.; Vilas-Vilela, J.L.; Lanceros-Méndez, S.; Reguera, J. Size Effect in Hybrid TiO 2 :Au Nanostars for Photocatalytic Water Remediation Applications. Int. J. Mol. Sci. 2022 , 23 , 13741. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Bhuskute, B.D.; Ali-Löytty, H.; Honkanen, M.; Salminen, T.; Valden, M. Influence of The Photodeposition Sequence on The Photocatalytic Activity of Plasmonic Ag-Au/TiO 2 Nanocomposites. Nanoscale Adv. 2022 , 4 , 4335–4343. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Huerta-Aguilar, C.A.; Palos-Barba, V.; Thangarasu, P.; Koodali, R.T. Visible Light Driven Photo-Degradation of Congo Red by TiO 2 -ZnO/Ag: DFT Approach on Synergetic Effect on Band Gap Energy. Chemosphere 2018 , 213 , 481–497. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Stojadinović, S.; Radić, N.; Vasilić, R.; Tadić, N.; Tsanev, A. Photocatalytic Degradation of Methyl Orange in The Presence of Transition Metals (Mn, Ni, Co) Modified TiO 2 Coatings Formed by Plasma Electrolytic Oxidation. Solid State Sci. 2022 , 129 , 106896. [ Google Scholar ] [ CrossRef ]
• Belošević-Čavor, J.; Koteski, V.; Umićević, A.; Ivanovski, V. Effect of 5d Transition Metals Doping on The Photocatalytic Properties of Rutile TiO 2 . Comput. Mater. Sci. 2018 , 151 , 328–337. [ Google Scholar ] [ CrossRef ]
• Meshram, A.A.; Sontakke, S.M. Rapid Degradation of Metamitron And Highly Complex Mixture of Pollutants Using MIL-53(Al) Integrated Combustion Synthesized TiO 2 . Adv. Powder Technol. 2021 , 32 , 3125–3135. [ Google Scholar ] [ CrossRef ]
• Zhu, Y. Enhanced Photoelectrochemical Properties of Fe-TiO 2 Nanotube Films: A Combined Experimental and Theoretical Study. Int. J. Electrochem. Sci. 2021 , 16 , 210662. [ Google Scholar ] [ CrossRef ]
• Mingmongkol, Y.; Trinh, D.T.T.; Phuinthiang, P.; Channei, D.; Ratananikom, K.; Nakaruk, A.; Khanitchaidecha, W. Enhanced Photocatalytic and Photokilling Activities of Cu-Doped TiO 2 Nanoparticles. Nanomater 2022 , 12 , 1198. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Rao, T.N.; Babji, P.; Parvatamma, B.; Naidu, T.M. Decontamination of Pesticide Residues in Water Samples Using Copper and Zinc Co-Doped Titania Nanocatalyst. Environ. Eng. Manag. J. 2020 , 19 , 721–731. [ Google Scholar ] [ CrossRef ]
• Sukhadeve, G.K.; Gedam, R.S. Visible Light Assisted Photocatalytic Degradation of Mixture of Reactive Ternary Dye Solution by Zn–Fe Co-Doped TiO 2 Nanoparticles. Chemosphere 2023 , 341 , 139990. [ Google Scholar ] [ CrossRef ]
• Liu, X. Preparation of Rare Earth Doped Modified TiO 2 Nanocrystalline Materials and Their Photocatalytic Properties. Master’s Thesis, Changji College, Xinjiang, China, 2022. [ Google Scholar ]
• Shi, Z.M.; Jin, L.N. Influence of La 3+ /Ce 3+ -Doping on Phase Transformation and Crystal Growth in TiO 2 -15wt% Zno Gels. J. Non-Cryst. Solids 2009 , 355 , 213–220. [ Google Scholar ] [ CrossRef ]
• Ricci, P.C.; Carbonaro, C.M.; Geddo Lehmann, A.; Congiu, F.; Puxeddu, B.; Cappelletti, G.; Spadavecchia, F. Structure and Photoluminescence of TiO 2 Nanocrystals Doped and Co-Doped with N and Rare Earths (Y 3+ , Pr 3+ ). J. Alloys Compd. 2013 , 561 , 109–113. [ Google Scholar ] [ CrossRef ]
• Hassan, M.S.; Amna, T.; Yang, O.B.; Kim, H.-C.; Khil, M.-S. TiO 2 Nanofibers Doped with Rare Earth Elements and Their Photocatalytic Activity. Ceram. Int. 2012 , 38 , 5925–5930. [ Google Scholar ] [ CrossRef ]
• Wen, M.; Yang, H.; Tong, L.; Yuan, L. Study on Degradation of Gold-Cyanide Wastewater by Rare-Earth La Doped TiO 2 -MnO 2 Composite Photocatalyst. Mol. Catal. 2023 , 550 , 113506. [ Google Scholar ] [ CrossRef ]
• ReszczyŃska, J.; Grzyb, T.; Sobczak, J.W.; Lisowski, W.; Gazda, M.; Ohtani, B.; Zaleska, A. Visible Light Activity of Rare Earth Metal Doped (Er 3+ , Yb 3+ Or Er 3+ /Yb 3+ ) Titania Photocatalysts. Appl. Catal. B Environ. 2015 , 163 , 40–49. [ Google Scholar ] [ CrossRef ]
• Tang, X.; Xue, Q.; Qi, X.; Cheng, C.; Yang, M.; Yang, T.; Chen, F.; Qiu, F.; Quan, X. DFT and Experimental Study on Visible-Light Driven Photocatalysis of Rare-Earth-Doped TiO 2 . Vacuum 2022 , 200 , 110972. [ Google Scholar ] [ CrossRef ]
• Zhou, F.; Yan, C.; Sun, Q.; Komarneni, S. TiO 2 /Sepiolite Nanocomposites Doped with Rare Earth Ions: Preparation, Characterization and Visible Light Photocatalytic Activity. Microporous Mesoporous Mater. 2019 , 274 , 25–32. [ Google Scholar ] [ CrossRef ]
• Kobwittaya, K.; Oishi, Y.; Torikai, T.; Yada, M.; Watari, T.; Luitel, H.N. Bright Red Upconversion Luminescence from Er 3+ and Yb 3+ Co-Doped Zno-TiO 2 Composite Phosphor Powder. Ceram. Int. 2017 , 43 , 13505–13515. [ Google Scholar ] [ CrossRef ]
• Ćurković, L.; Briševac, D.; Ljubas, D.; Mandić, V.; Gabelica, I. Synthesis, Characterization, and Photocatalytic Properties of Sol-Gel Ce-TiO 2 Films. Processes 2024 , 12 , 1144. [ Google Scholar ] [ CrossRef ]
• Benammar, I.; Salhi, R.; Deschanvres, J.-L.; Maalej, R. The Effect Of Rare Earth (Er, Yb) Element Doping On The Crystallization Of Y 2 Ti 2 O 7 Pyrochlore Nanoparticles Developed by Hydrothermal-Assisted-Sol-Gel Method. J. Solid State Chem. 2023 , 320 , 123856. [ Google Scholar ] [ CrossRef ]
• Arévalo-Pérez, J.C.; Cruz-Romero, D.D.L.; Cordero-García, A.; Lobato-García, C.E.; Aguilar-Elguezabal, A.; Torres-Torres, J.G. Photodegradation of 17 A-Methyltestosterone Using TiO 2 -Gd 3+ and TiO 2 -Sm 3+ Photocatalysts and Simulated Solar Radiation As An Activation Source. Chemosphere 2020 , 249 , 126497. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Kuwik, M.; Kowalska, K.; Pisarska, J.; Kochanowicz, M.; Żmojda, J.; Dorosz, J.; Dorosz, D.; Pisarski, W.A. Influence of TiO 2 Concentration on Near-Infrared Emission of Germanate Glasses Doped with Tm 3+ and Tm 3+ /Ho 3+ Ions. Ceram. Int. 2023 , 49 , 41090–41097. [ Google Scholar ] [ CrossRef ]
• Alzahrani, J.S.; Alrowaili, Z.A.; Eke, C.; Olarinoye, I.O.; Al-Buriahi, M.S. Characterization and Applications of Highly Optical Transparency Tellurite Glasses Doped with Er 3+ , Tm 3+ , And Nd 3+ . Optik 2023 , 281 , 170825. [ Google Scholar ] [ CrossRef ]
• Pascariu, P.; Cojocaru, C.; Homocianu, M.; Samoila, P. Tuning of Sm 3+ and Er 3+ -doped TiO 2 nanofibers for enhancement of the photocatalytic performance: Optimization of the photodegradation conditions. J. Environ. Manag. 2022 , 316 , 115317. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Guetni, I.; Belaiche, M.; Ferdi, C.A.; Oulhakem, O.; Alaoui, K.B.; Zaoui, F.; Bahije, L. Novel modified nanophotocatalysts of TiO 2 nanoparticles and TiO 2 /Alginate beads with lanthanides [La, Sm, Y] to degrade the Azo dye Orange G under UV-VIS radiation. Mater. Sci. Semicond. Process. 2024 , 174 , 108193. [ Google Scholar ] [ CrossRef ]
• Ren, Y.; Han, Y.; Li, Z.; Liu, X.; Zhu, S.; Liang, Y.; Yeung, K.W.K.; Wu, S. Ce and Er Co-doped TiO 2 for rapid bacteria- killing using visible light. Bioact. Mater. 2020 , 5 , 201–209. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Seshaiah, K.V.; Dileep, R.K.; Easwaramoorthi, R.; Ganapathy, V.; Kumar, R.S.S. Deciphering the role of (Er 3+ /Nd 3+ ) co-doping effect on TiO 2 as an improved electron transport layer in perovskite solar cells. Sol. Energy 2023 , 262 , 111801. [ Google Scholar ]
• Guo, Y.T.; Wang, H.Q. Research on Rare Earth Lanthanum-Doped Nanotitanium Dioxide Composite Fresh Packaging Films. Mater. Guide 2018 , 32 , 4357–4362. [ Google Scholar ]
• Li, J.; Zhang, X.; Tan, Z.; Wei, X.; Zhou, X. Effect of Lanthanum and Graphene Oxide Doping on The Photocatalytic Performance of TiO 2 . Chem. New Mater. 2023 , 51 , 159–163+168. [ Google Scholar ]
• Alanazi, H.E.; Emran, K.M. Nd-Gd–Platinum Doped TiO 2 Nanotube Arrays Catalyst for Water Splitting in Alkaline Medium. Int. J. Electrochem. Sci. 2023 , 18 , 100112. [ Google Scholar ] [ CrossRef ]
• Mei, Q.F.; Zhang, F.; Wang, N.; Lu, W.; Su, X.; Wang, W.; Wu, R. Titanium Dioxide-Based Z-Type Heterojunction Photocatalysts. J. Inorg. Chem. 2019 , 35 , 1321–1339. [ Google Scholar ]
• Qi, K.; Liu, N.; Cui, N.; Song, J.; Ma, Y.; Chen, Q. Design of Modified Titanium Dioxide Photocatalyst. J. Shenyang Norm. Univ. (Nat. Sci. Ed.) 2021 , 39 , 103–108. [ Google Scholar ]
• Hou, J.; Wang, Y.; Zhou, J.; Lu, Y.; Liu, Y.; Lv, X. Photocatalytic Degradation Of Methylene Blue Using A ZnO/TiO 2 Heterojunction Nanomesh Electrode. Surf. Interfaces 2021 , 22 , 100889. [ Google Scholar ] [ CrossRef ]
• Wang, D. Preparation and Photocatalytic Properties of TiO 2 /ZnO Micro- and Nanomaterials and Core-Shell Structures. Ph.D. Thesis, University of Chinese Academy of Sciences (Changchun Institute of Optical Precision Machinery and Physics, Chinese Academy of Sciences), Beijing, China, 2018. [ Google Scholar ]
• Yu, J.; Wang, S.; Low, J.; Xiao, W. Enhanced Photocatalytic Performance of Direct Z-Scheme G-C 3 N 4 -TiO 2 Photocatalysts for The Decomposition of Formaldehyde in Air. Phys. Chem. Chem. Phys. PCCP 2013 , 15 , 16883–16890. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Wongburapachart, C.; Pornaroontham, P.; Kim, K.; Rangsunvigit, P. Photocatalytic Degradation of Acid Orange 7 by NiO-TiO 2 /TiO 2 Bilayer Film Photo-Chargeable Catalysts. Coatings 2023 , 13 , 141. [ Google Scholar ] [ CrossRef ]
• Bai, N.; Liu, X.; Li, Z.; Ke, X.; Zhang, K.; Wu, Q. High-efficiency TiO 2 /ZnO nanocomposites photocatalysts by sol–gel and hydrothermal methods. J. Sol-Gel Sci. Technol. 2021 , 99 , 92–100. [ Google Scholar ] [ CrossRef ]
• Wittawat, R.; Rittipun, R.; Jarasfah, M.; Nattaporn, B. Synthesis of ZnO/TiO 2 Spherical Particles for Blue Light Screening by Ultrasonic Spray Pyrolysis. Mater. Today Commun. 2020 , 24 , 101126. [ Google Scholar ]
• Wang, S.; Li, X.; Li, D. Microwave Assisted Synthesis Of ZnO-TiO 2 and Its Visible Light Catalytic Denitrification Activity. J. Fuel Chem. Technol. 2023 , 51 , 589–598. [ Google Scholar ] [ CrossRef ]
• Ali, M.M.; Haque, M.J.; Kabir, M.H.; Kaiyum, M.A.; Rahman, M.S. Nano Synthesis Of ZnO–TiO 2 Composites by Sol-Gel Method and Evaluation of Their Antibacterial, Optical and Photocatalytic Activities. Results Mater. 2021 , 11 , 100199. [ Google Scholar ] [ CrossRef ]
• Abumousa, R.A.; Bououdina, M.; Ben Aissa, M.A.; Khezami, L.; Modwi, A. Efficient photocatalytic degradation of Congo red and other dyes by ternary TiO 2 /Y 2 O 3 @g-C 3 N 4 nanohybrid. J. Mater. Sci. Mater. Electron. 2024 , 35 , 486. [ Google Scholar ] [ CrossRef ]
• Heltina, D.; Imamatul Mastura, D.; Amri, A.; Peratenta Sembiring, M. Komalasari, Comparison of Synthesis Methods on TiO 2 -Graphene Composites for Photodegradation of Compound Waste. Mater. Today Proc. 2023 , 87 , 293–298. [ Google Scholar ] [ CrossRef ]
• Wang, S.; Li, X.; Wu, J. Preparation of TiO 2 /Graphene Oxide and Their Photocatalytic Properties at Room Temperature. J. Fuel Chem. Technol. 2022 , 50 , 1307–1316. [ Google Scholar ] [ CrossRef ]
• Kusiak-Nejman, E.; Wanag, A.; Kapica-Kozar, J.; Kowalczyk, Ł.; Zgrzebnicki, M.; Tryba, B.; Przepiórski, J.; Morawski, A.W. Methylene Blue Decomposition on TiO 2 /Reduced Graphene Oxide Hybrid Photocatalysts Obtained by A Two-Step Hydrothermal and Calcination Synthesis. Catal. Today 2020 , 357 , 630–637. [ Google Scholar ] [ CrossRef ]
• Zhou, M.; Jiang, Y.; Xie, Y.; Xie, D.L.; Mei, Y. Research progress on the preparation and modification of titanium dioxide nanoparticles and their application in polymer matrix composites. J. Compos. Mater. 2022 , 39 , 2089–2105. [ Google Scholar ]
• Maeda, S.; Fujita, M.; Idota, N.; Matsukawa, K.; Sugahara, Y. Preparation of Transparent Bulk TiO 2 /Pmma Hybrids with Improved Refractive Indices Via An In Situ Polymerization Process Using TiO 2 Nanoparticles Bearing Pmma Chains Grown by Surface-Initiated Atom Transfer Radical Polymerization. ACS Appl. Mater. Interfaces 2016 , 8 , 34762–34769. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Shi, Y.; Zhang, Q.; Liu, Y. Preparation of amphiphilic TiO 2 Janus particles with highly enhanced photocatalytic activity. Chin. J. Catal. 2019 , 40 , 786–794. [ Google Scholar ] [ CrossRef ]
• Nair, V.R.; Shetty Kodialbail, V. Floating bed reactor for visible light induced photocatalytic degradation of Acid Yellow 17 using polyaniline-TiO 2 nanocomposites immobilized on polystyrene cubes. Environ. Sci. Pollut. Res. 2020 , 27 , 14441–14453. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Chien, H.; Chen, X.; Tsai, W. Poly(Methyl Methacrylate)/Titanium Dioxide (Pmma/TiO 2 ) Nanocomposite with Shark-Skin Structure for Preventing Biofilm Formation. Mater. Lett. 2021 , 285 , 129098. [ Google Scholar ] [ CrossRef ]
• Neves, J.C.; Mohallem, N.D.; Viana, M. Polydimethylsiloxanes-Modified TiO 2 Coatings: The Role of Structural, Morphological and Optical Characteristics in A Self-Cleaning Surface. Ceram. Int. 2020 , 46 Pt B , 11606–11616. [ Google Scholar ] [ CrossRef ]
• Abdul, M.; Shahid, R.M.; Ghulam, M.M.; Tehreem, A.; Imran, S.; Maryum, R.; Aqsa, N. Fabrication of Ag–TiO 2 nanocomposite employing dielectric barrier discharge plasma for photodegradation of methylene blue. Phys. B Condens. Matter 2023 , 665 , 414995. [ Google Scholar ]
• Dong, S.; Tebbutt, G.T.; Millar, R.; Grobert, N.; Maciejewska, B.M. Hierarchical porosity design enables highly recyclable and efficient Au/TiO 2 composite fibers for photodegradation of organic pollutants. Mater. Des. 2023 , 234 , 112318. [ Google Scholar ] [ CrossRef ]
• Reguero-Márquez, G.A.; Lunagómez-Rocha, M.A.; Cervantes-Uribe, A.; Del Angel, G.; Rangel, I.; Torres-Torres, J.G.; González, F.; Godavarthi, S.; Arevalo-Perez, J.C.; de Los Monteros, A.E.; et al. Photodegradation of 2,4-D (dichlorophenoxyacetic acid) with Rh/TiO2; comparative study with other noble metals (Ru, Pt, and Au). RSC Adv. 2022 , 12 , 25711–25721. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Solmaz, F.; Aziz, H.; Rafael, L. Preparation of TiO 2 /Fe-MOF n–n heterojunction photocatalysts for visible-light degradation of tetracycline hydrochloride. Chemosphere 2023 , 336 , 139101. [ Google Scholar ]
• Muhammad, I.; Rab, N.; Akbar, K.J.; Habib, U.; Tahir, H.; Stanislaw, L.; Saifur, R.; Jerzy, J.; Alsaiar, M.A.; Asif, K.M.K.; et al. Synthesis and Characterization of Manganese-Modified Black TiO 2 Nanoparticles and Their Performance Evaluation for the Photodegradation of Phenolic Compounds from Wastewater. Materials 2021 , 14 , 7422. [ Google Scholar ] [ CrossRef ]
• Eleni, E.; Zoi, C.; Athanasios, T.; Kyriakos, B.; Pavlina, T.; Daniel, S.; Anastasia, K.; Lambropoulou, D.A. Photocatalytic degradation of a mixture of eight antibiotics using Cu-modified TiO 2 photocatalysts: Kinetics, mineralization, antimicrobial activity elimination and disinfection. J. Environ. Chem. Eng. 2021 , 9 , 105295. [ Google Scholar ]
• Cho, H.; Joo, H.; Kim, H.; Kim, J.-E.; Kang, K.-S.; Yoon, J. Improved photoelectrochemical properties of TiO 2 nanotubes doped with Er and effects on hydrogen production from water splitting. Chemosphere 2021 , 267 , 129289. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Rajeev, Y.N.; Magdalane, C.M.; Hepsibha, S.; Ramalingam, G.; Kumar, B.A.; Kumar, L.B.; Sangaraju, S. Europium decorated hierarchical TiO 2 heterojunction nanostructure with enhanced UV light photocatalytic activity for degradation of toxic industrial effluent. Inorg. Chem. Commun. 2023 , 157 , 111339. [ Google Scholar ] [ CrossRef ]
• Hu, L.; Xing, M.; He, X.; Yang, K.; Zhu, J.; Wang, J.; He, J.; Shi, J. Photocatalytic degradation of tetracycline hydrochloride by ZnO/TiO 2 composite photocatalyst. J. Mater. Sci. Mater. Electron. 2023 , 34 , 2273. [ Google Scholar ] [ CrossRef ]
• Huang, F.; Hao, H.; Sheng, W.; Lang, X. Dye-TiO 2 /SiO 2 assembly photocatalysis for blue light-initiated selective aerobic oxidation of organic sulfides. Chem. Eng. J. 2021 , 423 , 129419. [ Google Scholar ] [ CrossRef ]
• Yang, J.; Huang, Q.; Sun, Y.; An, G.; Li, X.; Mao, J.; Wei, C.; Yang, B.; Li, D.; Tao, T. Photocatalytic oxidation of formaldehyde under visible light using BiVO 4 -TiO 2 synthesized via ultrasonic blending. Environ. Sci. Pollut. Res. Int. 2024 , 31 , 30085–30098. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Paula, L.F.; Hofer, M.; Lacerda, V.P.B. Unraveling the photocatalytic properties of TiO 2 /WO 3 mixed oxides. Photochem. Photobiol. Sci. 2019 , 18 , 2469–2483. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Zhang, J.; Wang, C.; Shi, X.; Feng, Q.; Shen, T.; Wang, S. Modulation of the Structure of the Conjugated Polymer TMP and the Effect of Its Structure on the Catalytic Performance of TMP–TiO 2 under Visible Light: Catalyst Preparation, Performance and Mechanism. Materials 2023 , 16 , 1563. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Abu-Melha, S. Distinguishable photocatalytic activity of nano polyaniline with quantum dots metal oxide as photocatalysts for photodegradation of Dianix blue dye and different industrial pollutants. Polyhedron 2024 , 252 , 116781. [ Google Scholar ] [ CrossRef ]
• Meng, A.; Cheng, B.; Tan, H.; Fan, J.; Su, C.; Yu, J. TiO 2 /polydopamine S-scheme heterojunction photocatalyst with enhanced CO 2 -reduction selectivity. Appl. Catal. B Environ. 2021 , 289 , 120039. [ Google Scholar ] [ CrossRef ]

Share and Cite

Mao, T.; Zha, J.; Hu, Y.; Chen, Q.; Zhang, J.; Luo, X. Research Progress of TiO 2 Modification and Photodegradation of Organic Pollutants. Inorganics 2024 , 12 , 178. https://doi.org/10.3390/inorganics12070178

Mao T, Zha J, Hu Y, Chen Q, Zhang J, Luo X. Research Progress of TiO 2 Modification and Photodegradation of Organic Pollutants. Inorganics . 2024; 12(7):178. https://doi.org/10.3390/inorganics12070178

Mao, Tan, Junyan Zha, Ying Hu, Qian Chen, Jiaming Zhang, and Xueke Luo. 2024. "Research Progress of TiO 2 Modification and Photodegradation of Organic Pollutants" Inorganics 12, no. 7: 178. https://doi.org/10.3390/inorganics12070178

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Testing the Waters: EPA Researchers Study the Changing Nitrogen Landscape in Streams

Published June 25, 2024

Air quality regulations such as the Clean Air Act have led to improved air quality over the last several decades. One example of these improvements is the decline in nitrogen and sulfur atmospheric deposition across many areas of the United States.

Atmospheric deposition is a broad term that includes the transfer of materials from the atmosphere to the Earth’s surface. Acidic deposition (or acid rain) occurs when precipitation and particles with acidic components such as carbonic, sulfuric, or nitric acid fall to the ground from the atmosphere in wet or dry forms. Acid rain’s ecological effects can be clearly seen in aquatic environments, such as streams and lakes where they can be harmful to fish and other organisms. Since atmospheric deposition contains nitrogen, excessive deposition can acidify as well as cause an enrichment of the watershed’s nutrients, which can affect the water’s biological and chemical processes .

“We know that the Clean Air Act, especially the 1990 amendments, has caused substantial reductions in nitrogen deposition in many watersheds, especially in the eastern U.S.,” EPA researcher Jana Compton said. “Our question was, ‘Do we see improvements in water quality associated with the changes in nitrogen inputs from air sources?’”

To explore this question, a team of researchers including former Oak Ridge Institute for Science and Education (ORISE) post-doctoral fellow Jiajia Lin, EPA researchers Jana Compton, Robert Sabo, Ryan Hill, Marc Weber, J. Renée Brooks, Steve Paulsen and John Stoddard, and Alan Herlihy from Oregon State University, published “ The changing nitrogen landscape of United States streams: Declining deposition and increasing organic nitrogen .” The paper explores the relationship between deposition and water chemistry in small streams in the eastern contiguous U.S., where atmospheric deposition is the major nitrogen source for the watersheds.

The researchers used National Rivers and Streams Assessment (NRSA) monitoring data from the National Aquatic Resource Survey to analyze stream chemistry; the series of surveys sampled thousands of streams across the contiguous U.S., from 2000 to 2014. For purposes of this study, target “streams” were identified as flowing waters that were wadeable, generally meaning one could walk through the current.

Then, the team used the National Nutrient Inventory , a set of databases that identify the potential types and sizes of nutrient pollution sources in a specific location, to determine where among these streams atmospheric deposition was the largest nitrogen input. The researchers conducted statistical analyses to examine how nitrogen inputs and water chemistry changed over time. Using the NRSA statistical approach for population estimates, the findings were extrapolated to different regions across the contiguous U.S.

The study’s results illustrate a complex story about the current nitrogen landscape in U.S streams and more research is needed to better understand the implications. In eastern U.S. watersheds, change analysis showed that atmospheric nitrogen deposition declined: a testament to the Clean Air Act’s impact. Researchers observed small and non-significant declines in nitrate in streams; however, dissolved organic carbon and total organic nitrogen increased. Organic carbon and nitrogen are produced in terrestrial and aquatic ecosystems and can be influenced by ecosystem productivity and soil properties. The changes in total organic nitrogen concentrations indicate an increase in the mobilization of organic nitrogen, or the amount of organic nitrogen that was released from the landscape and moved to the water. In addition, watershed organic nitrogen was exported at a faster pace than organic carbon. One “downstream” impact of increasing organic carbon and nitrogen is the need for added treatment and potential formation of disinfection byproducts in drinking water systems. 

Meet Our Researchers

Meet EPA Ecologist Jana Compton, Ph.D.

Meet Our Other Ecosystem Researchers

While streams in the eastern U.S. may be recovering from acidification due to reductions in acid deposition resulting from Clean Air Act amendments, the study signals that other biological or chemical processes may be impeding these improvements. Possible drivers behind these processes may include soil recovery from acidification, changes in carbon availability, or varying climate conditions in the watershed.

Now that the researchers discovered a pattern with increasing organic nitrogen, their findings set the foundation to continue monitoring these nutrient trends.

“We cannot really say with certainty what the cause is for these changes in stream nitrogen. What this paper does show is the strong and significant increase in organic nitrogen levels in these streams,” Compton said. “We found a widespread pattern and we need to better understand it to understand the possible outcomes and impacts.”

EPA researchers are working to compile data about nutrient inputs in water bodies to understand water quality and predict the impacts on watersheds from human activities.

Learn More About the Science

Changing nitrogen landscape of United States streams: Declining deposition and increasing organic nitrogen

Basic Information on Nutrient Pollution

National Aquatic Resource Surveys

National Nutrient Inventory Portfolio

National Lakes Assessment

National Rivers and Streams Assessment

Nutrients and Harmful Algal Blooms Research

Shifts in the Composition of Nitrogen Deposition in the Conterminous United States are Discernable in Stream Chemistry

Tools and Resources Webinar: Nutrient Explorer (March 13, 2024)

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IGNIITE 2024 Selectees

ARPA-E announced approximately $11.5 million in funding through its new Inspiring Generations of New Innovators to Impact Technologies in Energy 2024 (IGNIITE 2024) program focused on early-career scientists and engineers converting disruptive ideas into impactful energy technologies. Each IGNIITE 2024 awardee will receive approximately $500,000 to advance research projects at universities, national laboratories, and in the private sector that will span the full spectrum of energy applications, including advanced energy storage systems, fusion reactor technology, carbon-negative concrete alternatives, power electronics for grid reliability, critical material recovery, energy-efficient water desalination, plastic depolymerization, and more. Read more in the press release here . 

The following individuals selected through IGNIITE 2024 are:

University of California, Berkeley – Berkeley, CA

Jessica Boles is an assistant professor in electrical engineering at the University of California, Berkeley, and co-director of the recently launched Berkeley Power and Energy Center. Boles will explore a new class of power electronics based on modular piezoelectric components, which are capable of enabling order-of-magnitude scale miniaturization and significant gains in efficiency for power electronics in a wide variety of applications.

Project: High-Performance, Modular Piezoelectric Components for Miniaturized Power Conversion – Award Amount: $500,000    

Syracuse University – Syracuse, NY

Craig Cahillane is an assistant professor at Syracuse University with a background in gravitational wave detection. In this project, Cahillane will build a novel prototype for neutral beam injection in fusion reactors. The work will support the development of electricity generation and storage for enabling fusion power generation and new advancements in lasers and materials technologies.

Project: Ultra-High Power Photoneutralization Cavity for Neutral Beam Injection in Fusion Reactors – Award Amount: $500,000 

Duke University – Durham, NC

Liang Feng is an assistant professor at Duke University in mechanical engineering and materials science. Feng is developing a process to convert plastic waste, such as plastic bottles and bags, into adsorbents to capture carbon dioxide. The approach seeks to take advantage of the tough and long-lasting nature of plastics to create carbon-dioxide sponges with high porosity and durability.  

Project: Upgrading Plastic Waste into Low-Cost Porous Adsorbents for Direct Air Capture – Award Amount: $500,000 

Rensselaer Polytechnic Institute – Troy, NY

Fudong Han currently holds the Priti and Mukesh Chatter ’82 Career Development Chair Assistant Professorship at Rensselaer Polytechnic Institute. Han aims to develop a low-cost solid-state battery that enables cleaner, safer, and more efficient electric aircraft. This project leverages Han’s recent discovery utilizing halide-based solid electrolytes.

Project: Critical Metal-Free, Conversion-Type Solid-State Batteries for Advanced Air Mobility – Award Amount: $500,000   

National Renewable Energy Laboratory – Golden, CO

Nelson James is a researcher in the National Renewable Energy Laboratory’s advanced building equipment research group. James will develop a proof-of-concept prototype of a multifunctional heat pump to reduce building heating and cooling emissions and improve building energy resilience. This will be accomplished through new compression approaches and system designs.

Project: Electrochemically Looping Adsorptive Heat Pumps for Next-Generation Building Decarbonization – Award Amount: $499,922

Katrina (Kat) Knauer is a researcher at the National Renewable Energy Laboratory, the CTO of the BOTTLE Consortium, and an assistant adjoint professor at the University of Colorado, Boulder. Knauer will focus on a new process for mixed, variable bio-based polyester waste streams based on a volatile amine catalyzed methanolysis process. This technology will reduce reliance on both fossil fuels and agricultural feedstocks.

Project: Mixed Polyester Deconstruction & Monomer Recovery to Enable a Circular Bioeconomy – Award Amount: $499,999

University of Wisconsin–Madison – Madison, WI

Sebastian Kube is an assistant professor in materials science and engineering at the University of Wisconsin–Madison. The objective of Kube’s project is to build an autonomous laboratory platform, “AlloyBot,” which will develop new structural alloys for energy and propulsion technologies. AlloyBot will synthesize and test 100 new alloy compositions per week with minimal human assistance.

Project: AlloyBot: Autonomous Platform to Develop Alloys for Energy and Propulsion Technologies 100x Faster – Award Amount: $500,000 

Michigan State University – East Lansing, MI

Woongkul Lee is an assistant professor in electrical and computer engineering at Michigan State University. The objective of Lee’s research is to develop an optically powered ultra-high-speed wound-field synchronous generator for uncrewed aircraft. The generator will be integrated with an optical encoder for position estimation to maximize its power density, reliability, and power handling capability.

Project: Optically Powered Ultra-high-Speed (OPUS) Wound-Field Synchronous Generators – Award Amount: $500,000 

Jinxing Li is an assistant professor in the Department of Biomedical Engineering and the Institute for Quantitative Health Science and Engineering at Michigan State University. In this project, Li aims to reduce carbon emissions associated with both building materials and construction methods through 3D robotic bioprinting of biogenic concrete structures to create next-generation sustainable and intelligent buildings.

Project: Robotic 3D Bioprinting of Entire Building Structures Using Biogenic Concrete – Award Amount: $500,000 

Peregrine Hydrogen – Santa Cruz, CA

Rain (Ruperto) Mariano is Director of Cell Development at Peregrine Hydrogen, focused on delivering green hydrogen without the premium. Mariano’s objective is to develop an electrolysis technology to provide affordable hydrogen by cutting the energy intensity of water electrolysis in half. If successful, the technology has the potential to decarbonize highly polluting hydrogen used in industry today by providing a cost-competitive alternative.

Project: Advanced Electrolysis Architectures for Low-Cost Green Hydrogen – Award Amount: $500,000  

Luca Mastropasqua is an assistant professor in mechanical engineering at the University of Wisconsin-Madison. Mastropasqua seeks to transform the waste plastic upcycling process by studying, developing, and characterizing an innovative solid-state electrochemical membrane reactor and its thermal integration. This will be achieved through high-temperature electrochemical hydrogenative depolymerization of long amorphous and semi-crystalline polymers.

Project: Direct High-Temperature Electrochemical Hydrogenative Depolymerization for Waste Plastic Upcycling – Award Amount: $500,000 

Paul Meyer is a researcher at the National Renewable Energy Laboratory. In this project, Meyer seeks to develop a lignin-based concrete alternative for buildings and construction to address major challenges facing this industrial sector. The project will explore different types of lignin, the effects on chemical reactions and drying times, and pathways to large-scale commercialization.

Project: BUILD’EM: Chemistry, Performance, and Path to Market of a Cement-less Construction Material – Award Amount: $499,989   

Lawrence Berkeley National Laboratory – Berkeley, CA

Justin Panich leads a research group at Lawrence Berkeley National Laboratory and is a deputy director at the Joint BioEnergy Institute. In this project, Panich will develop a bioelectrocatalytic cell that converts renewable energy, carbon dioxide, and nitrogen gas into ammonia. The team will maximize microbes for ammonia production through bioengineering strategies and integrate the microbes into an electrolysis-coupled growth chamber.

Project: Carbon-Negative and Ambient Production of Fertilizer Precursor – Award Amount: $497,151 

Lydia Rachbauer is a scientist in biological systems and engineering at Lawrence Berkeley National Laboratory. Rachbauer aims to develop a scalable and sustainable carbon conversion process to minimize greenhouse gas emissions in the aviation sector. The approach leverages the microbial conversion of waste-derived syngas into the C6-carboxylic acid caproate as a precursor for sustainable aviation fuels.

Project: C1 Bioconversion Platform: Integrating Acetogenic Consortia for Circular Economy Solutions in Sustainable Fuel Production, Industrial Efficiency, and Decarbonization – Award Amount: $499,501

University of Washington – Seattle, WA

Julie Rorrer is an assistant professor of chemical engineering at the University of Washington. In this project, Rorrer will harness plastic waste to produce liquid organic hydrogen carriers, addressing plastic pollution and hydrogen storage needs simultaneously. The process uses an adaptive catalytic reactor that converts various plastic wastes using different modes depending on the availability of hydrogen.

Project: Development of an Adaptive Catalytic Reactor to Store Intermittent Green Hydrogen Using Plastic Waste – Award Amount: $500,000

ChemFinity Technologies – Brooklyn, NY

Adam Uliana is the co-founder and CEO of ChemFinity Technologies, a cleantech startup in Brooklyn, NY, that spun out of University of California, Berkeley in 2022. Uliana is developing new processes to recycle critical minerals by leveraging ChemFinity’s porous sorbent material technology. The approach selectively recovers many critical minerals from wastes, including e-waste, spent catalytic converters, and other sources.

Project: Tunable Porous Polymer Networks with Unprecedented Efficiency in Recovering Critical Metals – Award Amount: $500,000

University of Alabama – Tuscaloosa, AL

Zhongyang Wang is an assistant professor in chemical and biological engineering at the University of Alabama. Wang will use sodium borohydride as a liquid fuel for a direct borohydride fuel cell to empower marine vessels. Sodium borohydride is readily transportable using existing infrastructure, and no greenhouse gases would be generated during the operation of the liquid-liquid fuel cell.

Project: Tailoring Bipolar Membrane Interfaces to Boost Direct Borohydride Fuel Cell Performance for Marine Transportation Applications – Award Amount: $499,803 

University of California-Irvine – Irvine, CA

Xizheng (Zoe) Wang is an assistant professor in mechanical and aerospace engineering at the University of California, Irvine. Wang will investigate a better method to produce multi-elemental nanodisks to enable scalable clean hydrogen production. The electrified vapor deposition method will produce nanodisks that can reduce or eliminate the usage of precious metals for a more robust and sustainable supply chain.

Project: High-Entropy Nanodisks by Ultrafast Electrified Vapor Deposition for Hydrogen Production – Award Amount: $500,000 

University of Nebraska-Lincoln – Lincoln, NE

Jun Wang is an assistant professor in electrical and computer engineering at the University of Nebraska-Lincoln. Wang is developing solutions to enhance power grid resilience through a first-of-its-kind 10-kilovolt high-frequency press-pack silicon-carbide MOSFET module. The module will have 30 times faster switching frequency and 5 times higher power density than the state of the art.

Project: Multicell Electrical-Transient-Accelerated Press-Pack Modules (METAPAK) – Award Amount: $500,000 

Oak Ridge National Laboratory – Oak Ridge, TN

Andrew Westover is a staff scientist at Oak Ridge National Laboratory with a focus on solid-state batteries. Westover’s project will develop bulk ionic glasses (BIG) using traditional glass processing that captures the desirable ductility of LiPON glass. The ultimate project goal is demonstrating lithium-metal anode charging/discharging using a BIG electrolyte separator, a traditional cathode, and a Li metal anode.

Project: Ductile Bulk Ionic Glasses for Electric Vehicle Batteries (BIGBATT) – Award Amount: $500,000 

Battelle Energy Alliance (Idaho National Laboratory) – Idaho Falls, ID

Michael Woods is a research scientist at Idaho National Laboratory with over ten years of experience in molten salt experimentation. Woods’ project will investigate the use of brazing for joining salt-facing materials for molten salt energy technologies, including nuclear molten salt reactors and thermal energy storage systems.

Project: Performance of Brazed Materials for Molten Salt Energy Technologies – Award Amount: $500,000 

Guang Yang is a member of the energy storage and conversion group at Oak Ridge National Laboratory. Yang is working to revolutionize energy storage by creating a groundbreaking battery that uses low-cost materials like sodium and carbon dioxide. The battery could be up to 40 times more powerful and 90% cheaper than current technologies.

Project: Supercritical Carbon Dioxide-Leveraged Redox Flow Batteries (SUPERCOOL-RFB) – Award Amount: $500,000 

University of California, Santa Barbara – Santa Barbara, CA

Yangying Zhu is an assistant professor in mechanical engineering at the University of California, Santa Barbara. Zhu will develop a desalination system using solar thermal energy and multi-stage distillation. The work will enhance thermal transport processes to utilize energy more efficiently, which can significantly reduce energy consumption compared to existing industrial desalination processes.

Project: Solar Thermal Membrane Desalination via Thin-film Phase Change – Award Amount: $500,000