acid rain

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acid rain
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{{Use mdy dates|date=February 2019}}{{other uses}}{{pp-semi-indef}}{{pp-move-indef}}(File:Origins of acid rain.svg|thumb|upright=1.2|Processes involved in acid deposition (only SO2 and NOx play a significant role in acid rain).)File:Cloud formation from refinery in Curacao.jpg|thumb|Acid clouds can grow on SO2 emissions from refineries, as seen here in CuraçaoCuraçao{{external media | width = 210px | align = right | headerimage= | audio1 = "Whatever Happened to Acid Rain?", Science History Institute}}Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals and infrastructure. Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids. Some governments have made efforts since the 1970s to reduce the release of sulfur dioxide and nitrogen oxide into the atmosphere with positive results. Nitrogen oxides can also be produced naturally by lightning strikes, and sulfur dioxide is produced by volcanic eruptions. Acid rain has been shown to have adverse impacts on forests, freshwaters and soils, killing insect and aquatic life-forms, causing paint to peel, corrosion of steel structures such as bridges, and weathering of stone buildings and statues as well as having impacts on human health.


"Acid rain" is a popular term referring to the deposition of a mixture from wet (rain, snow, sleet, fog, cloudwater, and dew) and dry (acidifying particles and gases) acidic components. Distilled water, once carbon dioxide is removed, has a neutral pH of 7. Liquids with a pH less than 7 are acidic, and those with a pH greater than 7 are alkaline. "Clean" or unpolluted rain has an acidic pH, but usually no lower than 5.7, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid according to the following reaction:
{{Chemical formula|H|2|O}} (l) + {{Chemical formula |C||O|2}} (g) {{eqm}} {{Chemical formula|H|2|C||O|3}} (aq)
Carbonic acid then can ionize in water forming low concentrations of carbonate and hydronium ions:
{{Chemical formula|H|2|O}} (l) + {{Chemical formula|H|2|C||O|3}} (aq) {{eqm}} {{Chemical formula|H||C||O|3}}− (aq) + {{Chemical formula|H|3|O}}+ (aq)
Unpolluted rain can also contain other chemicals which affect its pH (acidity level). A common example is nitric acid produced by electric discharge in the atmosphere such as lightning.JOURNAL, 10.1029/JD092iD11p13299, Likens, Gene E., Keene, William C., Miller, John M., Galloway, James N., Chemistry of precipitation from a remote, terrestrial site in Australia, 1987, Journal of Geophysical Research, 92, D11, 13299, 1987JGR....9213299L, Acid deposition as an environmental issue (discussed later in the article) would include additional acids other than {{Chemical formula|H|2|C||O|3}}.


The corrosive effect of polluted, acidic city air on limestone and marble was noted in the 17th century by John Evelyn, who remarked upon the poor condition of the Arundel marbles.E. S. de Beer, ed. The Diary of John Evelyn, III, 1955 (September 19, 1667) p. 495.Since the Industrial Revolution, emissions of sulfur dioxide and nitrogen oxides into the atmosphere have increased.{{Citation
|title=Glossary |at=acid rain |publisher=NASA Earth Observatory |location=United States |url= |accessdate=February 15, 2013 |archiveurl= |archivedate=December 13, 2011 |url-status=live }}Weathers, K. C. and Likens, G. E. (2006). "Acid rain", pp. 1549–1561 in: W. N. Rom and S. Markowitz (eds.). Environmental and Occupational Medicine. Lippincott-Raven Publ., Philadelphia. Fourth Edition, {{ISBN|0-7817-6299-5}}. In 1852, Robert Angus Smith was the first to show the relationship between acid rain and atmospheric pollution in Manchester, England.Seinfeld, John H.; Pandis, Spyros N (1998). Atmospheric Chemistry and Physics â€” From Air Pollution to Climate Change. John Wiley and Sons, Inc. {{ISBN|978-0-471-17816-3}}
In the late 1960s scientists began widely observing and studying the phenomenon.JOURNAL, Likens, G. E., Bormann, F. H., Johnson, N. M., 1972, Acid rain, Environment, 14, 2, 33–40, 10.1080/00139157.1972.9933001, The term "acid rain" was coined in 1872 by Robert Angus Smith.Acid Rain in New England, A Brief History {{webarchive |url= |date=September 25, 2010 }}. Retrieved on February 9, 2013. Canadian Harold Harvey was among the first to research a "dead" lake. At first the main focus in research lay on local effects of acid rain. Waldemar Christofer Brøgger was the first to acknowledge long-distance transportation of pollutants crossing borders from the United Kingdom to Norway.JOURNAL, Brøgger, Waldemar Christofer, 1881, Note on a contaminated snowfall under the heading Mindre meddelelser (Short communications), Naturen, 5, 47, Public awareness of acid rain in the US increased in the 1970s after The New York Times published reports from the Hubbard Brook Experimental Forest in New Hampshire of the harmful environmental effects that result from it.JOURNAL, Likens, G. E., Bormann, F. H., 10.1126/science.184.4142.1176, Acid Rain: A Serious Regional Environmental Problem, 1974, Science, 184, 4142, 1176–9, 17756304, 1974Sci...184.1176L, JOURNAL, 10.1029/2005JG000157, Soil CO2 dynamics and fluxes as affected by tree harvest in an experimental sand ecosystem, 2006, Keller, C. K., White, T. M., O'Brien, R., Smith, J. L., Journal of Geophysical Research, 111, G3, G03011, 2006JGRG..111.3011K, Occasional pH readings in rain and fog water of well below 2.4 have been reported in industrialized areas. Industrial acid rain is a substantial problem in China and RussiaJOURNAL, 17835740, 1987, Galloway, JN, Dianwu, Z, Jiling, X, Likens, GE, Acid rain: China, United States, and a remote area, 236, 4808, 1559–62, 10.1126/science.236.4808.1559, Science, 1987Sci...236.1559G, WEB, Chandru,weblink CHINA: Industrialization pollutes its country side with Acid Rain,, September 9, 2006, November 18, 2010, dead,weblink" title="">weblink June 20, 2010, and areas downwind from them. These areas all burn sulfur-containing coal to generate heat and electricity.{{Citation
|last=Lefohn |first=A.S. |last2=Husar |first2=J.D. |last3=Husar |first3=R.B. |year=1999 |title=Global Sulfur Emissions Database |publisher=A.S.L. & Associates |location=United States |url= }}
The problem of acid rain has not only increased with population and industrial growth, but has become more widespread. The use of tall smokestacks to reduce local pollution has contributed to the spread of acid rain by releasing gases into regional atmospheric circulation.JOURNAL, Likens, G. E., Wright, R. F., Galloway, J. N., Butler, T. J., 1979, Acid rain, Scientific American, 241, 4, 43–51, 10.1038/scientificamerican1079-43, 1979SciAm.241d..43L, JOURNAL, Likens, G. E., 1984, Acid rain: the smokestack is the "smoking gun", Garden, 8, 4, 12–18, Often deposition occurs a considerable distance downwind of the emissions, with mountainous regions tending to receive the greatest deposition (because of their higher rainfall). An example of this effect is the low pH of rain which falls in Scandinavia.

In the United States

{{external media | width = 190px | align = right | headerimage= (File:Gene Likens 2015 Mariel Carr.JPG|100px) |audio1= “Whatever Happened to Acid Rain?“, Distillations Podcast, Science History Institute }}File:Bixi stele (wrapped), Harvard University, Cambridge, MA - IMG 4607.JPG|thumb|Since 1998, Harvard University wraps some of the bronze and marble statues on its campus, such as this "(Harvard Bixi|Chinese stele]]", with waterproof covers every winter, in order to protect them from corrosion caused by acid rain and acid snow"Art Under Wraps", Harvard Magazine, March–April 2000)The earliest report about acid rain in the United States was from the chemical evidence from Hubbard Brook Valley. In 1972, a group of scientists including Gene Likens discovered the rain that was deposited at White Mountains of New Hampshire was acidic. The pH of the sample was measured to be 4.03 at Hubbard Brook.JOURNAL, Likens, Gene E., Bormann, F. Herbert, Johnson, Noye M., Acid Rain, (Environment: Science and Policy for Sustainable Development), 14, 2, 33–40, 10.1080/00139157.1972.9933001, 1972, The Hubbard Brook Ecosystem Study followed up with a series of research that analyzed the environmental effects of acid rain. Acid rain that mixed with stream water at Hubbard Brook was neutralized by the alumina from soils.JOURNAL, Johnson, Noye M., Driscoll, Charles T., Eaton, John S., Likens, Gene E., McDowell, William H., September 1, 1981, 'Acid rain', dissolved aluminum and chemical weathering at the Hubbard Brook Experimental Forest, New Hampshire, Geochimica et Cosmochimica Acta, 45, 9, 1421–1437, 10.1016/0016-7037(81)90276-3, 1981GeCoA..45.1421J, The result of this research indicates the chemical reaction between acid rain and aluminum leads to increasing rate of soil weathering. Experimental research was done to examine the effects of increased acidity in stream on ecological species. In 1980, a group of scientists modified the acidity of Norris Brook, New Hampshire, and observed the change in species' behaviors. There was a decrease in species diversity, an increase in community dominants, and a decrease in the food web complexity.JOURNAL, Hall, Ronald J., Likens, Gene E., Fiance, Sandy B., Hendrey, George R., August 1, 1980, Experimental Acidification of a Stream in the Hubbard Brook Experimental Forest, New Hampshire, Ecology (journal), Ecology, en, 61, 4, 976–989, 10.2307/1936765, 1939-9170, 1936765, In 1980, the US Congress passed an Acid Deposition Act.JOURNAL,weblink Lackey, R.T., 1997, Science, policy, and acid rain: lessons learned, Renewable Resources Journal, 15, 1, 9–13, This Act established an 18-year assessment and research program under the direction of the National Acidic Precipitation Assessment Program (NAPAP). NAPAP looked at the entire problem from a scientific perspective. It enlarged a network of monitoring sites to determine how acidic the precipitation actually was, and to determine long-term trends, and established a network for dry deposition. It looked at the effects of acid rain and funded research on the effects of acid precipitation on freshwater and terrestrial ecosystems, historical buildings, monuments, and building materials. It also funded extensive studies on atmospheric processes and potential control programs.From the start, policy advocates from all sides attempted to influence NAPAP activities to support their particular policy advocacy efforts, or to disparage those of their opponents. For the US Government's scientific enterprise, a significant impact of NAPAP were lessons learned in the assessment process and in environmental research management to a relatively large group of scientists, program managers and the public.JOURNAL, 10.1016/S1462-9011(98)00006-9, Acid rain: Science and policy making, 1998, Winstanley, Derek, Lackey, Robert T., Warnick, Walter L., Malanchuk, John, Environmental Science & Policy, 1, 51, In 1981, the National Academy of Sciences was looking into research about the controversial issues regarding acid rain.NEWS,weblink ACID RAIN ISSUE CREATES STRESS BETWEEN ADMINISTRATION AND SCIENCE ACADEMY, Times, Robert Reinhold, Special To The New York, June 8, 1982, The New York Times, 0362-4331, November 16, 2016, President Ronald Reagan did not place a huge attention on the issues of acid rainWEB,weblink Ronald Reagan on Environment,, November 16, 2016, until his personal visit to Canada and confirmed that Canadian border suffered from the drifting pollution from smokestacks in Midwest of US. Reagan honored the agreement to Canadian Prime Minister Pierre Trudeau’s enforcement of anti-pollution regulation.WEB,weblink HYSTERIA ABOUT ACID RAIN Even Ronald Reagan now casts it as the villain. He is overriding a lot of scientific evidence. - April 14, 1986,, November 16, 2016, In 1982, US President Ronald Reagan commissioned William Nierenberg to serve on the National Science Board.WEB,weblink Ronald Reagan: Nomination of William A. Nierenberg To Be a Member of the National Science Board,, November 16, 2016, Nierenberg selected scientists including Gene Likens to serve on a panel to draft a report on acid rain. In 1983, the panel of scientists came up with a draft report, which concluded that acid rain is a real problem and solutions should be sought.WEB,weblink Report of the Acid Rain Peer Review Panel, July 1984, Document Display {{!, NEPIS {{!}} US EPA|language=en|access-date=November 16, 2016}} White House Office of Science and Technology Policy reviewed the draft report and sent Fred Singer’s suggestions of the report, which cast doubt on the cause of acid rain.NEWS,weblink From tobacco to climate change, ‘merchants of doubt’ undermined the science, April 17, 2010, Grist, en-US, November 16, 2016, The panelists revealed rejections against Singer’s positions and submitted the report to Nierenberg in April. In May 1983, the House of Representatives voted against legislation that aimed to control sulfur emissions. There was a debate about whether Nierenberg delayed to release the report. Nierenberg himself denied the saying about his suppression of the report and explained that the withheld of the report after the House's vote was due to the fact that the report was not ready to be published.NEWS,weblink LEGISLATORS SAT WHITE HOUSE SUPPRESSED ACID RAIN REPORT, Franklin, Ben A., August 18, 1984, The New York Times, 0362-4331, November 16, 2016, In 1991, the US National Acid Precipitation Assessment Program (NAPAP) provided its first assessment of acid rain in the United States.The US National Acid Precipitation Assessment Program : 1990 integrated assessment report. Washington, D.C. : National Acid Precipitation Assessment Program, Office of the Director, [1991] It reported that 5% of New England Lakes were acidic, with sulfates being the most common problem. They noted that 2% of the lakes could no longer support Brook Trout, and 6% of the lakes were unsuitable for the survival of many species of minnow. Subsequent Reports to Congress have documented chemical changes in soil and freshwater ecosystems, nitrogen saturation, decreases in amounts of nutrients in soil, episodic acidification, regional haze, and damage to historical monuments.Meanwhile, in 1990, the US Congress passed a series of amendments to the Clean Air Act.WEB,weblink Clean Air Act Title IV - Subchapter A: Acid Deposition Control | Overview of the Clean Air Act and Air Pollution | US EPA,, June 3, 2015, March 20, 2018, Title IV of these amendments established the a cap and trade system designed to control emissions of sulfur dioxide and nitrogen oxides.John Bachmann, David Calkins, Margo Oge. “Cleaning the Air We Breathe: A Half Century of Progress.” EPA Alumni Association. September 2017. Pages 26-27. Title IV called for a total reduction of about 10 million tons of SO2 emissions from power plants, close to a 50% reduction. It was implemented in two phases. Phase I began in 1995, and limited sulfur dioxide emissions from 110 of the largest power plants to a combined total of 8.7 million tons of sulfur dioxide. One power plant in New England (Merrimack) was in Phase I. Four other plants (Newington, Mount Tom, Brayton Point, and Salem Harbor) were added under other provisions of the program. Phase II began in 2000, and affects most of the power plants in the country.During the 1990s, research continued. On March 10, 2005, the EPA issued the Clean Air Interstate Rule (CAIR). This rule provides states with a solution to the problem of power plant pollution that drifts from one state to another. CAIR will permanently cap emissions of SO2 and NOx in the eastern United States. When fully implemented, CAIR will reduce SO2 emissions in 28 eastern states and the District of Columbia by over 70% and NOx emissions by over 60% from 2003 levels.WEB,weblink US EPA: A Brief History of Acid Rain, United States Environmental Protection Agency, 2002, November 18, 2010, dead,weblink" title="">weblink September 25, 2010, Overall, the program's cap and trade program has been successful in achieving its goals. Since the 1990s, SO2 emissions have dropped 40%, and according to the Pacific Research Institute, acid rain levels have dropped 65% since 1976.'Cap-and-trade' model eyed for cutting greenhouse gases, San Francisco Chronicle, December 3, 2007.WEB,weblink Facts On File News Services Databases,, November 18, 2010, {{dead link|date=October 2016 |bot=InternetArchiveBot |fix-attempted=yes }} Conventional regulation was used in the European Union, which saw a decrease of over 70% in SO2 emissions during the same time period.Gilberston, T. and Reyes, O. 2009. Carbon Trading: how it works and why it fails. Dag Hammarskjöld Foundation: 22In 2007, total SO2 emissions were 8.9 million tons, achieving the program's long-term goal ahead of the 2010 statutory deadline.Acid Rain Program 2007 Progress Report, United States Environmental Protection Agency, January 2009.In 2007 the EPA estimated that by 2010, the overall costs of complying with the program for businesses and consumers would be $1 billion to $2 billion a year, only one fourth of what was originally predicted. Forbes says: "In 2010, by which time the cap and trade system had been augmented by the George W. Bush administration's Clean Air Interstate Rule, SO2 emissions had fallen to 5.1 million tons."WEB, Gerdes, Justin, Cap and Trade Curbed Acid Rain: 7 Reasons Why It Can Do The Same For Climate Change,weblink Forbes, Forbes, October 27, 2014, The term citizen science can be traced back as far as January 1989 and a campaign by the Audubon Society to measure acid rain. Scientist Muki Haklay cites in a policy report for the Wilson Center entitled 'Citizen Science and Policy: A European Perspective' a first use of the term 'citizen science' by R. Kerson in the magazine MIT Technology Review from January 1989.WEB, Muki Haklay, Citizen Science and Policy: A European Perspective,weblink Woodrow Wilson International Center for Scholars, 11, 2015, June 3, 2016, MAGAZINE, R. Kerson, Lab for the Environment, MIT Technology Review, 1989, 92, 1, 11–12, Quoting from the Wilson Center report: "The new form of engagement in science received the name "citizen science". The first recorded example of the use of the term is from 1989, describing how 225 volunteers across the US collected rain samples to assist the Audubon Society in an acid-rain awareness raising campaign. The volunteers collected samples, checked for acidity, and reported back to the organization. The information was then used to demonstrate the full extent of the phenomenon."

Emissions of chemicals leading to acidification

The most important gas which leads to acidification is sulfur dioxide. Emissions of nitrogen oxides which are oxidized to form nitric acid are of increasing importance due to stricter controls on emissions of sulfur compounds. 70 Tg(S) per year in the form of SO2 comes from fossil fuel combustion and industry, 2.8 Tg(S) from wildfires and 7–8 Tg(S) per year from volcanoes.Berresheim, H.; Wine, P.H. and Davies D.D. (1995). "Sulfur in the Atmosphere". In Composition, Chemistry and Climate of the Atmosphere, ed. H.B. Singh. Van Nostrand Rheingold {{ISBN|0-442-01264-0}}

Natural phenomena

{{Bar chart|title=Mean acidifying emissions (air pollution) of different foods per 100g of proteinJOURNAL, Nemecek, T., Poore, J., 2018-06-01, Reducing food’s environmental impacts through producers and consumers,weblink Science, 360, 6392, 987–992, 10.1126/science.aaq0216, 0036-8075, 29853680, |float=right|label_type=Food Types|data_type=Acidifying Emissions (g SO2eq per 100g protein)|bar_width=20|width_units=em|data_max=300.6|label1=Beef|data1=343.6|label2=Cheese|data2=165.5|label3=Pork|data3=142.7|label4=Lamb and Mutton|data4=139.0|label5=Farmed Crustaceans|data5=133.1|label6=Poultry|data6=102.4|label7=Farmed Fish|data7=65.9|label8=Eggs|data8=53.7|label9=Groundnuts|data9=22.6|label10=Peas|data10=8.5|label11=Tofu|data11=6.7|label12=|data12=|label13=|data13=}}The principal natural phenomena that contribute acid-producing gases to the atmosphere are emissions from volcanoes. Thus, for example, fumaroles from the Laguna Caliente crater of Poás Volcano create extremely high amounts of acid rain and fog, with acidity as high as a pH of 2, clearing an area of any vegetation and frequently causing irritation to the eyes and lungs of inhabitants in nearby settlements. Acid-producing gasses are also created by biological processes that occur on the land, in wetlands, and in the oceans. The major biological source of sulfur compounds is dimethyl sulfide.Nitric acid in rainwater is an important source of fixed nitrogen for plant life, and is also produced by electrical activity in the atmosphere such as lightning.WEB,weblink Acid Rain: Causes, Effects and Solutions, July 14, 2018, August 23, 2019, Acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe.Soils of coniferous forests are naturally very acidic due to the shedding of needles, and the results of this phenomenon should not be confused with acid rain.

Human activity

{{See also|Nitrogen cycle|Human impact on the nitrogen cycle|sulfur cycle}}File:Gavin Power Plant.jpg|thumb|The coal-fired Gavin Power Plant in Cheshire, OhioCheshire, OhioThe principal cause of acid rain is sulfur and nitrogen compounds from human sources, such as electricity generation, animal agriculture, factories, and motor vehicles. Electrical power generation using coal is among the greatest contributors to gaseous pollution responsible for acidic rain. The gases can be carried hundreds of kilometers in the atmosphere before they are converted to acids and deposited. In the past, factories had short funnels to let out smoke but this caused many problems locally; thus, factories now have taller smoke funnels. However, dispersal from these taller stacks causes pollutants to be carried farther, causing widespread ecological damage.

Chemical processes

Combustion of fuels produces sulfur dioxide and nitric oxides. They are converted into sulfuric acid and nitric acid.Clean Air Act Reduces Acid Rain In Eastern United States, ScienceDaily, September 28, 1998

Gas phase chemistry

In the gas phase sulfur dioxide is oxidized by reaction with the hydroxyl radical via an intermolecular reaction:
SO2 + OH· → HOSO2·
which is followed by:
HOSO2· + O2 → HO2· + SO3
In the presence of water, sulfur trioxide (SO3) is converted rapidly to sulfuric acid:
SO3 (g) + H2O (l) → H2SO4 (aq)
Nitrogen dioxide reacts with OH to form nitric acid:(File:Air Pollution-Causes&Effects.svg|thumb|This shows the process of the air pollution being released into the atmosphere and the areas that will be affected.)
NO2 + OH· → HNO3

Chemistry in cloud droplets

When clouds are present, the loss rate of SO2 is faster than can be explained by gas phase chemistry alone. This is due to reactions in the liquid water droplets.
Sulfur dioxide dissolves in water and then, like carbon dioxide, hydrolyses in a series of equilibrium reactions:
SO2 (g) + H2O {{eqm}} SO2·H2O SO2·H2O {{eqm}} H+ + HSO3− HSO3− {{eqm}} H+ + SO32−
There are a large number of aqueous reactions that oxidize sulfur from S(IV) to S(VI), leading to the formation of sulfuric acid. The most important oxidation reactions are with ozone, hydrogen peroxide and oxygen (reactions with oxygen are catalyzed by iron and manganese in the cloud droplets).

Acid deposition

Wet deposition

Wet deposition of acids occurs when any form of precipitation (rain, snow, and so on.) removes acids from the atmosphere and delivers it to the Earth's surface. This can result from the deposition of acids produced in the raindrops (see aqueous phase chemistry above) or by the precipitation removing the acids either in clouds or below clouds. Wet removal of both gases and aerosols are both of importance for wet deposition.

Dry deposition

Acid deposition also occurs via dry deposition in the absence of precipitation. This can be responsible for as much as 20 to 60% of total acid deposition.WEB,weblink UK National Air Quality Archive: Air Pollution Glossary,, April 1, 2002, November 18, 2010, dead,weblink" title="">weblink April 17, 2009, This occurs when particles and gases stick to the ground, plants or other surfaces.

Adverse effects

Acid rain has been shown to have adverse impacts on forests, freshwaters and soils, killing insect and aquatic life-forms as well as causing damage to buildings and having impacts on human health.

Surface waters and aquatic animals

(File:Waterspecies.gif|thumb|Not all fish, shellfish, or the insects that they eat can tolerate the same amount of acid; for example, frogs can tolerate water that is more acidic (i.e., has a lower pH) than trout.)Both the lower pH and higher aluminium concentrations in surface water that occur as a result of acid rain can cause damage to fish and other aquatic animals. At pH lower than 5 most fish eggs will not hatch and lower pH can kill adult fish. As lakes and rivers become more acidic biodiversity is reduced. Acid rain has eliminated insect life and some fish species, including the brook trout in some lakes, streams, and creeks in geographically sensitive areas, such as the Adirondack Mountains of the United States.US EPA: Effects of Acid Rain – Surface Waters and Aquatic Animals However, the extent to which acid rain contributes directly or indirectly via runoff from the catchment to lake and river acidity (i.e., depending on characteristics of the surrounding watershed) is variable. The United States Environmental Protection Agency's (EPA) website states: "Of the lakes and streams surveyed, acid rain caused acidity in 75% of the acidic lakes and about 50% of the acidic streams". Lakes hosted by silicate basement rocks are more acidic than lakes within limestone or other basement rocks with a carbonate composition (i.e. marble) due to buffering effects by carbonate minerals, even with the same amount of acid rain.BOOK, Mineral Resources, Economics and the Environment., Kesler, Stephen, Cambridge University, 2015, 9781107074910, {{Citation needed|date=February 2018}}


Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are unable to tolerate changes to low pH and are killed.Rodhe, H., et al. The global distribution of acidifying wet deposition. Environmental Science and TEchnology. vlo. 36, no. 20 (October) p. 4382–8 The enzymes of these microbes are denatured (changed in shape so they no longer function) by the acid. The hydronium ions of acid rain also mobilize toxins, such as aluminium, and leach away essential nutrients and minerals such as magnesium.US EPA: Effects of Acid Rain – Forests {{webarchive |url= |date=July 26, 2008 }}
2 H+ (aq) + Mg2+ (clay) {{eqm}} 2 H+ (clay) + Mg2+ (aq)
Soil chemistry can be dramatically changed when base cations, such as calcium and magnesium, are leached by acid rain thereby affecting sensitive species, such as sugar maple (Acer saccharum).JOURNAL, The biogeochemistry of sulfur at Hubbard Brook,weblink 10.1023/A:1020972100496, 2002, Likens, G.E., Driscoll, C.T., Buso, D.C., Mitchell, M.J., Lovett, G.M., Bailey, S.W., Siccama, T.G., Reiners, W.A., Alewell, C., Biogeochemistry, 60, 3, 235, JOURNAL, 10.1126/science.272.5259.244,weblink Long-Term Effects of Acid Rain: Response and Recovery of a Forest Ecosystem, 1996, Likens, G. E., Driscoll, C. T., Buso, D. C., Science, 272, 5259, 244, 1996Sci...272..244L,

Forests and other vegetation

File:Acid rain woods1.JPG|thumb|Acid rain can have severe effects on vegetation. A forest in the Black Triangle in Europe.]]Adverse effects may be indirectly related to acid rain, like the acid's effects on soil (see above) or high concentration of gaseous precursors to acid rain. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain.Other plants can also be damaged by acid rain, but the effect on food crops is minimized by the application of lime and fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the case of wilderness lands. When calcium is leached from the needles of red spruce, these trees become less cold tolerant and exhibit winter injury and even death.DeHayes, D.H., Schaberg, P.G. and G.R. Strimbeck. (2001). Red Spruce Hardiness and Freezing Injury Susceptibility. In: F. Bigras, ed. Conifer Cold Hardiness. Kluwer Academic Publishers, the Netherlands {{ISBN|0-7923-6636-0}}.JOURNAL, Lazarus, Brynne E., Schaberg, Paul G., Hawley, Gary J., DeHayes, Donald H., 2006, Landscape-scale spatial patterns of winter injury to red spruce foliage in a year of heavy region-wide injury, Can. J. For. Res., 36, 142–152,weblink 10.1139/x05-236, weblink" title="">highbeam copy

Ocean acidification

{{expand section|date=July 2013}}Acid rain has a much less harmful effect on the oceans. Acid rain can cause the ocean's pH to fall, making it more difficult for different coastal species to create their exoskeletons that they need to survive. These coastal species link together as part of the ocean's food chain and without them being a source for other marine life to feed off of more marine life will die.WEB,weblink Acid Rain Has Disproportionate Impact on Near-Shore Ocean Waters - Windows to the Universe,, Coral's limestone skeletal is sensitive to pH drop, because the calcium carbonate, core component of the limestone dissolves in acidic (low pH) solutions.

Human health effects

Acid rain does not directly affect human health. The acid in the rainwater is too dilute to have direct adverse effects. The particulates responsible for acid rain (sulfur dioxide and nitrogen oxides) do have an adverse effect. Increased amounts of fine particulate matter in the air contribute to heart and lung problems including asthma and bronchitis.Effects of Acid Rain – Human Health. (June 2, 2006). Retrieved on 2013-02-09.

Other adverse effects

(File:Pollution - Damaged by acid rain.jpg|Effect of acid rain on statues|thumb|right)(File:Skulptur aus Sandstein, Dresden 2012-09-06-0555.jpg|Acid rain and weathering|thumb|right)Acid rain can damage buildings, historic monuments, and statues, especially those made of rocks, such as limestone and marble, that contain large amounts of calcium carbonate. Acids in the rain react with the calcium compounds in the stones to create gypsum, which then flakes off.
CaCO3 (s) + H2SO4 (aq) {{eqm}} CaSO4 (s) + CO2 (g) + H2O (l)
The effects of this are commonly seen on old gravestones, where acid rain can cause the inscriptions to become completely illegible. Acid rain also increases the corrosion rate of metals, in particular iron, steel, copper and bronze.JOURNAL, ICP on effects on materials, 10.1007/BF01186242, 85, 4, Water, Air, & Soil Pollution, 2701–2706, 1995WASP...85.2701R, Reisener, A., Stäckle, B., Snethlage, R., 1995, WEB,weblink Approaches in modeling the impact of air pollution-induced material degradation, November 18, 2010,weblink" title="">weblink July 16, 2011, dead,

Affected areas

Places significantly impacted by acid rain around the globe include most of eastern Europe from Poland northward into Scandinavia,WEB,weblink Acid Rain in Europe, Ed. Hatier, 1993, January 31, 2010, United Nations Environment Programme GRID Arendal, dead,weblink" title="">weblink August 22, 2009, the eastern third of the United States,WEB,weblink Clean Air Markets 2008 Highlights, US Environmental Protection Agency, 2008, January 31, 2010, and southeastern Canada. Other affected areas include the southeastern coast of China and Taiwan.WEB,weblink Acid Rain - Green Education Foundation {{!, GEF {{!}} Sustainability Education||language=en-gb|access-date=November 2, 2017}}

Prevention methods

Technical solutions

Many coal-firing power stations use flue-gas desulfurization (FGD) to remove sulfur-containing gases from their stack gases. For a typical coal-fired power station, FGD will remove 95% or more of the SO2 in the flue gases. An example of FGD is the wet scrubber which is commonly used. A wet scrubber is basically a reaction tower equipped with a fan that extracts hot smoke stack gases from a power plant into the tower. Lime or limestone in slurry form is also injected into the tower to mix with the stack gases and combine with the sulfur dioxide present. The calcium carbonate of the limestone produces pH-neutral calcium sulfate that is physically removed from the scrubber. That is, the scrubber turns sulfur pollution into industrial sulfates.In some areas the sulfates are sold to chemical companies as gypsum when the purity of calcium sulfate is high. In others, they are placed in landfill. The effects of acid rain can last for generations, as the effects of pH level change can stimulate the continued leaching of undesirable chemicals into otherwise pristine water sources, killing off vulnerable insect and fish species and blocking efforts to restore native life.Fluidized bed combustion also reduces the amount of sulfur emitted by power production.Vehicle emissions control reduces emissions of nitrogen oxides from motor vehicles.

International treaties

International treaties on the long-range transport of atmospheric pollutants have been agreed for example, the 1985 Helsinki Protocol on the Reduction of Sulphur Emissions under the Convention on Long-Range Transboundary Air Pollution. Canada and the US signed the Air Quality Agreement in 1991. Most European countries and Canada have signed the treaties.

Emissions trading

{{See also|Acid Rain Program}}In this regulatory scheme, every current polluting facility is given or may purchase on an open market an emissions allowance for each unit of a designated pollutant it emits. Operators can then install pollution control equipment, and sell portions of their emissions allowances they no longer need for their own operations, thereby recovering some of the capital cost of their investment in such equipment. The intention is to give operators economic incentives to install pollution controls.The first emissions trading market was established in the United States by enactment of the Clean Air Act Amendments of 1990.Former Deputy Administrator Hank Habicht talks about management at EPA. An Interview with Hank Habicht Video, Transcript (see p6). December 21, 2012. The overall goal of the Acid Rain Program established by the ActClean Air Act Amendments of 1990, 42 U.S. Code 7651 is to achieve significant environmental and public health benefits through reductions in emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx), the primary causes of acid rain. To achieve this goal at the lowest cost to society, the program employs both regulatory and market based approaches for controlling air pollution.

See also



External links

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