Acid rain, from USGS Water-Science School Back to previous page Acid Rain: Do you need to start wearing a rain hat? 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. 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 (SO2) and nitrogen oxides (NOx) 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 (SO2). Exhausts from cars cause the formation of nitrogen oxides in the air. From these gases, airborne sulfuric acid (H2SO4) and nitric acid (HNO3) 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 (SO2), 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.

By the way, no, you don't need to start wearing a rain hat. Sources and more information Acid Rain - Causes, Effects, and Solutions Acid Rain The Causes, History, and Effects of Acid Rain The Union Camp Paper Mill on the Savannah River in Savannah, Georgia. Getty Images/VisionsofAmerica/Joe Sohm By Amanda Briney, Contributing Writer What Is Acid Rain? Acid rain is made up of water droplets that are unusually acidic because of atmospheric pollution, most notably the excessive amounts of sulfur and nitrogen released by cars and industrial processes. Acid rain is also called acid deposition because this term includes other forms of acidic precipitation such as snow. Acidic deposition occurs in two ways: wet and dry. Wet deposition is any form of precipitation that removes acids from the atmosphere and deposits them on the Earth’s surface. Dry deposition polluting particles and gases stick to the ground via dust and smoke in the absence of precipitation. This form of deposition is dangerous, however, because precipitation can eventually wash pollutants into streams, lakes, and rivers. Acidity itself is determined based on the pH level of the water droplets. PH is the scale measuring the amount of acid in the water and liquid.

The pH scale ranges from 0 to 14 with a lower pH being more acidic while a high pH is alkaline; seven is neutral. continue reading below our video What are the Seven Wonders of the World Normal rain water is slightly acidic and has a pH range of 5.3-6.0. Acid deposition is anything below that range. It is also important to note that the pH scale is logarithmic and each whole number on the scale represents a 10-fold change. Today, acid deposition is present in the northeastern United States, southeastern Canada, and much of Europe including portions of Sweden, Norway, and Germany. In addition, parts of South Asia, South Africa , Sri Lanka , and Southern India are all in danger of being impacted by acid deposition in the future. Causes and History of Acid Rain Acid deposition can be causes by natural sources like volcanoes, but it is mainly caused by the release of sulfur dioxide and nitrogen oxide during fossil fuel combustion. When these gases are discharged into the atmosphere, they react with the water, oxygen, and other gases already present there to form sulfuric acid, ammonium nitrate, and nitric acid.

These acids then disperse over large areas because of wind patterns and fall back to the ground as acid rain or other forms of precipitation. The gases most responsible for acid deposition are a byproduct of electric power generation and the burning of coal. As such, man-made acid deposition began becoming a significant issue during the Industrial Revolution and was first discovered by a Scottish chemist, Robert Angus Smith, in 1852. In that year, he discovered the relationship between acid rain and atmospheric pollution in Manchester, England. Although it was discovered in the 1800s, acid deposition did not gain significant public attention until the 1960s, and the term acid rain was coined in 1972. Public attention further increased in the 1970s when the New York Times published reports about problems occurring in the Hubbard Brook Experimental Forest in New Hampshire. Effects of Acid Rain After studying the Hubbard Brook Forest and other areas, researchers have found several important impacts of acid deposition on both natural and man-made environments. Aquatic settings are the most clearly impacted by acid deposition though because acidic precipitation falls directly into them. Both dry and wet deposition also runs off of forests, fields, and roads and flows into lakes, rivers, and streams.

As this acidic liquid flows into larger bodies of water, it is diluted, but over time, acids can accrue and lower the overall pH of the body of water. Acid deposition also causes clay soils to release aluminum and magnesium further lowering the pH in some areas. If the pH of a lake drops below 4.8, its plants and animals risk death. It is estimated that around 50,000 lakes in the United States and Canada have a pH below normal (about 5.3 for water). Several hundred of these have a pH too low to support any aquatic life. Aside from aquatic bodies, acid deposition can significantly impact forests. As acid rain falls on trees, it can make them lose their leaves, damage their bark, and stunt their growth. By damaging these parts of the tree, it makes them vulnerable to disease, extreme weather, and insects. Acid falling on a forest’s soil is also harmful because it disrupts soil nutrients, kills microorganisms in the soil, and can sometimes cause a calcium deficiency. Trees at high altitudes are also susceptible to problems induced by acidic cloud cover as the moisture in the clouds blankets them.

Damage to forests by acid rain is seen all over the world, but the most advanced cases are in Eastern Europe. It’s estimated that in Germany and Poland, half of the forests are damaged, while 30% in Switzerland have been affected. Finally, acid deposition also has an impact on architecture and art because of its ability to corrode certain materials. As acid lands on buildings (especially those constructed with limestone) it reacts with minerals in the stones sometimes causing them to disintegrate and wash away. Acid deposition can also cause concrete to deteriorate, and it can corrode modern buildings, cars, railroad tracks, airplanes, steel bridges, and pipes above and below ground. What's Being Done? Because of these problems and the adverse effects air pollution has on human health, a number of steps are being taken to reduce sulfur and nitrogen emissions. Most notably, many governments are now requiring energy producers to clean smoke stacks by using scrubbers which trap pollutants before they are released into the atmosphere and catalytic converters in cars to reduce their emissions. Additionally, alternative energy sources are gaining more prominence today, and funding is being given to the restoration of ecosystems damaged by acid rain worldwide. Follow this link for maps and animated maps of acid rain concentration in the United States.

Acid Rain Presentations Acid Rain “Acid rain” became a household term in the 1980s when unchecked emissions from industry and motor vehicles were blamed for causing environmental deterioration. Scientific evidence has linked acid rain to decreased fish and wildlife populations, degraded lakes and streams, and human health hazards. Although the term has since faded from public consciousness, acid rain is a complex and global problem that still exists today. What is Acid Rain? First identified in 1872 in Sweden and studied in the U.S. beginning in the 1950s, acid rain is precipitation in the form of rain, snow, hail, dew, or fog that transports sulfur and nitrogen compounds from the high atmosphere to the ground. Sulfur dioxide (SO2) and nitrogen oxides (NO, NO2) are bi-products from burning fuels in electric utilities and from other industrial and natural sources. These chemicals react with water, oxygen, carbon dioxide, and sunlight in the atmosphere to form sulfuric and nitric acids. The acids reach the ground and change the chemistry within the environment. The acidity of any solution is determined on the pH scale of 0 to 14.

A pH level of 0 to 7 is considered acidic; 7 is neural; and a level above 7 is alkaline. As the pH number decreases, acidity increases. Unopened bottled distilled water has a pH of 7, so it is neutral. In comparison, household ammonia is an alkaline with a pH of 11.5. Milk is slightly acidic with a 6.5 pH, and soft drinks, which contain phosphoric acid, have a 3.1 pH. Although the pH scale may seem straightforward, determining the pH of “normal” rain is much more complex. When distilled water is exposed to air, an interaction with carbon dioxide increases acidity through the formation of carbonic acid, H2CO3, and the pH level falls. Many scientists agree that the normal pH of rain is a slightly acidic 5.6 because of perpetual chemical interactions in the air. What’s more, rain pH levels can vary significantly over short distances and in a short amount of time, even during the same rainfall. Seasons, climate, and a host of other factors can also influence the acidity of rain. Rain and snow are not the only processes that deposit sulfur and nitrogen acids from the atmosphere to the ground.

These compounds are also present in gases and dry particles, which are more difficult to measure. Like wet deposition, the occurrence of “dry deposition” of acids varies in different areas, depending on distance from the emission source and climatic conditions. What Causes Acid Rain? Acid rain is linked to both natural and man-made sources. Nitrogen oxides are formed through the extreme heating of air when a thunderstorm produces lightning. Also, sulfurous gases are discharged from erupted volcanoes and rotting vegetation. However, most public attention has been focused on man-made sources of acid rain, which include the burning of any fuel that contains sulfur and nitrogen compounds, including public utilities, industrial broilers, motor vehicles, and chemical plants. Electric power generation accounted for 69 percent of total sulfur dioxide emissions in the U.S. in 2007 and 20 percent of nitrogen oxides, according to the U.S. Environmental Protection Agency (USEPA). Many industrial sources of sulfur dioxide are located in the eastern U.S., particularly in the Midwest and the Ohio Valley where coal combustion and power generation frequently occur. Typically, the highest nitrogen oxide emissions are found in states with large urban areas, a heavy population density, and significant automobile traffic.

Acid rain is not limited to the region where sources are located. Prevailing winds can blow chemicals in the atmosphere for hundreds or even thousands of miles before being deposited, regardless of state and country boundaries. For instance, compounds from industry in China can potentially be deposited in the U.S. Midwest. For this reason, acid rain is considered a global problem. What are its Effects? Acid rain has been linked to detrimental effects in the environment and in human health. Forests, lakes, and streams: Acid rain can cause widespread damage to trees. This is especially true of trees at high elevations in various regions of the U.S. Acidic deposition can damage leaves and also deplete nutrients in forest soils and in trees so that trees become more vulnerable to disease and environmental stress. When lakes and streams become more acidic than normal, they cannot continue to support the same types of fish and aquatic life as in the past. Fish communities dwindle due to high mortality, a reduced growth rate, skeletal deformities, and failed reproduction. Lakes ultimately become home only to species that can tolerate high-acid conditions. Game fish, such as trout, are particularly sensitive to acidic water conditions. A healthy lake has a pH of 6.5 or higher.

Only a few fish species can survive at a pH of below 5; at a pH of 4, the lake is considered dead. A decrease in fish populations is often the first sign of an acidification problem. Not all lakes are equally vulnerable to acid rain, however. In some areas, such as in Illinois, the average pH of a freshwater lake is an alkaline 8 to 9 because soils and rocks in the bottom and sides of the lake contain high levels of calcium and magnesium, which neutralize the acidity of rain. Lakes surrounded by granite, such as in New England and northern New York, don’t fare as well. Plants and crops: Acid rain can potentially reduce agricultural production by changing the chemical properties of soil, slowing the rate of microbiological processes, and reducing soil nutrients. Roots of natural vegetation and crops can become damaged due to stunted growth. Human effects: Acidic water moving through pipes causes lead and copper to leach into the water. Most public water suppliers remove such dangerous chemicals at the plant, but tainted water could be a problem for residents who don’t rely on public water supplies for their drinking water. Acidic fog can be more hazardous to health than acid rain as small droplets can be inhaled.

These atmospheric acids can cause respiratory problems in humans such as throat, nose, and eye irritation, headache, and asthma. Acid fog is particularly dangerous for the elderly, those who are ill, and people who have chronic respiratory conditions. Man-Made Materials: Although sunlight, heat, cold, and wind contribute to the deterioration of man-made structures and objects, acid deposition speeds up this process. Metal structures and vehicles become corroded, and limestone buildings, tombstones, statues, and monuments deteriorate faster when rain is acidic. How is Acid Precipitation Collected? Wet deposition samples can be measured to determine chemical concentrations in almost any area. The National Atmospheric Deposition Program (NADP) at the Illinois State Water Survey, University of Illinois, maintains three networks with more than 350 deposition monitoring sites. The NADP National Trends Network has 250 sites in the U.S. located far from the point sources of pollution. Each site has an automated precipitation collector and gage to gather samples only during rain or snowfall. Weekly samples are collected and sent to the NADP for analysis. The network measures acidity and calcium, magnesium, sodium, potassium, sulfate, nitrate, chloride, and ammonium ions.

Data are available online at . These monitoring efforts support research and policy on air quality issues. NADP monitoring data show that wet sulfate deposition has decreased an average of 30 percent since the early 1990s in the eastern United States. The largest decreases occurred in Maryland, New York, Virginia, West Virginia, and Pennsylvania. Nitrogen deposition has decreased as well, but to a lesser extent. Legislative mandates, federal government programs, and environmental-friendly changes in fossil fuel use in electrical power plants have successfully lowered the emission of SO2 and NOx and the resulting acid deposition in the U.S. since the 1980s. However, the problem still exists. Scientists continue to try to fully understand acid rain and its long-term effects on the environment and on human health. Bibliography American Chemical Society. 1982. Acid Rain. American Chemical Society. Washington, D.C. H. John Heinz III Center for Science, Economics and the Environment. 2008. The state of the nation’s ecosystems: 2008. The Heinz Center, Washington, D.C. Likens, G. (Lead Author); Environmental Protection Agency (Content source); W. Davis, L.

Zaikowski, and S. C. Nodvin (Topic Editors). 2007. Acid rain. In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). Stanitski, C. L., L. P. Eubanks, C. H. Middlecamp, and W.J. Stratton. 2000. Neutralizing the threat of acid rain. in Chemistry in Context (third ed.). American Chemical Society. U.S. Environmental Protection Agency. 2009, January. Acid rain and related programs: 2007 Progress Report. USEPA. Washington, D.C. (Additional information available at ) What is Acid Rain and What Causes It? Questia : Search over 400,000 books and journals at Questia online. FastWeb Free Scholarship Search : Find free money for college or an advanced degree. Adapted from "Acid Rain", Environmental Protection Agency August 6th, 2002 What is Acid Rain and What Causes It?

"Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry. Wet deposition refers to acidic rain, fog, and snow. As this acidic water flows over and through the ground, it affects a variety of plants and animals. The strength of the effects depend on many factors, including how acidic the water is, the chemistry and buffering capacity of the soils involved, and the types of fish, trees, and other living things that rely on the water. Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes, and trees. Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms. When that happens, the runoff water adds those acids to the acid rain, making the combination more acidic than the falling rain alone. Prevailing winds blow the compounds that cause both wet and dry acid deposition across state and national borders, and sometimes over hundreds of miles.

Scientists discovered, and have confirmed, that sulfur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acid rain. In the US, About 2/3 of all SO2 and 1/4 of all NOx comes from electric power generation that relies on burning fossil fuels like coal. Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of most of these reactions. The result is a mild solution of sulfuric acid and nitric acid. How Do We Measure Acid Rain? Acid rain is measured using a scale called "pH." The lower a substance's pH, the more acidic it is. Pure water has a pH of 7.0. Normal rain is slightly acidic because carbon dioxide dissolves into it, so it has a pH of about 5.5. As of the year 2000, the most acidic rain falling in the US has a pH of about 4.3. Acid rain's pH, and the chemicals that cause acid rain, are monitored by two networks, both supported by EPA.

The National Atmospheric Deposition Program measures wet deposition, and its Web site features maps of rainfall pH (follow the link to the isopleth maps) and other important precipitation chemistry measurements. The Clean Air Status and Trends Network (CASTNET) measures dry deposition. Its web site features information about the data it collects, the measuring sites, and the kinds of equipment it uses. Effects of Acid Rain Acid rain causes acidification of lakes and streams and contributes to damage of trees at high elevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation's cultural heritage. Prior to falling to the earth, SO2 and NOx gases and their particulate matter derivatives, sulfates and nitrates, contribute to visibility degradation and harm public health. What Society Can Do About Acid Deposition There are several ways to reduce acid deposition, more properly called acid deposition, ranging from societal changes to individual action.

Understand acid deposition's causes and effects To understand acid deposition's causes and effects and track changes in the environment, scientists from EPA, state governments, and academic study acidification processes. They collect air and water samples and measure them for various characteristics like pH and chemical composition, and they research the effects of acid deposition on human-made materials such as marble and bronze. Finally, scientists work to understand the effects of sulfur dioxide (SO2) and nitrogen oxides (NOx) - the pollutants that cause acid deposition and fine particles - on human health. To solve the acid rain problem, people need to understand how acid rain causes damage to the environment. They also need to understand what changes could be made to the air pollution sources that cause the problem. The answers to these questions help leaders make better decisions about how to control air pollution and therefore how to reduce - or even eliminate - acid rain. Since there are many solutions to the acid rain problem, leaders have a choice of which options or combination of options are best. The next section describes some of the steps that can be taken to reduce, or even eliminate, the acid deposition problem.

Clean up smokestacks and exhaust pipes Almost all of the electricity that powers modern life comes from burning fossil fuels like coal, natural gas, and oil. acid deposition is caused by two pollutants that are released into the atmosphere, or emitted, when these fuels are burned: sulfur dioxide (SO2) and nitrogen oxides (NOx). Coal accounts for most US sulfur dioxide (SO2) emissions and a large portion of NOx emissions. Sulfur is present in coal as an impurity, and it reacts with air when the coal is burned to form SO2. In contrast, NOx is formed when any fossil fuel is burned. There are several options for reducing SO2 emissions, including using coal containing less sulfur, washing the coal, and using devices called scrubbers to chemically remove the SO2 from the gases leaving the smokestack. Power plants can also switch fuels; for example burning natural gas creates much less SO2 than burning coal. Certain approaches will also have additional benefits of reducing other pollutants such as mercury and carbon dioxide. Understanding these "co-benefits" has become important in seeking cost-effective air pollution reduction strategies. Finally, power plants can use technologies that don't burn fossil fuels.

Each of these options has its own costs and benefits, however; there is no single universal solution. Similar to scrubbers on power plants, catalytic converters reduce NOx emissions from cars. These devices have been required for over twenty years in the US, and it is important to keep them working properly and tailpipe restrictions have been tightened recently. EPA has also made, and continues to make, changes to gasoline that allows it to burn cleaner. Use alternative energy sources There are other sources of electricity besides fossil fuels. They include: nuclear power, hydropower, wind energy, geothermal energy, and solar energy. Of these, nuclear and hydropower are used most widely; wind, solar, and geothermal energy have not yet been harnessed on a large scale in this country. There are also alternative energies available to power automobiles, including natural gas powered vehicles, battery-powered cars, fuel cells, and combinations of alternative and gasoline powered vehicles. All sources of energy have environmental costs as well as benefits. Some types of energy are more expensive to produce than others, which means that not all Americans can afford all types of energy.

Nuclear power, hydropower, and coal are the cheapest forms today, but changes in technologies and environmental regulations may shift that in the future. All of these factors must be weighed when deciding which energy source to use today and which to invest in for tomorrow. Restore a damaged environment Acid deposition penetrates deeply into the fabric of an ecosystem, changing the chemistry of the soil as well as the chemistry of the streams and narrowing, sometimes to nothing, the space where certain plants and animals can survive. Because there are so many changes, it takes many years for ecosystems to recover from acid deposition, even after emissions are reduced and the rain becomes normal again. For example, while the visibility might improve within days, and small or episodic chemical changes in streams improve within months, chronically acidified lakes, streams, forests, and soils can take years to decades or even centuries (in the case of soils) to heal. However, there are some things that people do to bring back lakes and streams more quickly. Limestone or lime (a naturally-occurring basic compound) can be added to acidic lakes to "cancel out" the acidity. This process, called liming, has been used extensively in Norway and Sweden but is not used very often in the United States.

Liming tends to be expensive, has to be done repeatedly to keep the water from returning to its acidic condition, and is considered a short-term remedy in only specific areas rather than an effort to reduce or prevent pollution. Furthermore, it does not solve the broader problems of changes in soil chemistry and forest health in the watershed, and does nothing to address visibility reductions, materials damage, and risk to human health. However, liming does often permit fish to remain in a lake, so it allows the native population to survive in place until emissions reductions reduce the amount of acid deposition in the area. Look to the future As emissions from the largest known sources of acid deposition - power plants and automobiles-are reduced, EPA scientists and their colleagues must assess the reductions to make sure they are achieving the results Congress anticipated. If these assessments show that acid deposition is still harming the environment, Congress may begin to consider additional ways to reduce emissions that cause acid deposition. They may consider additional emissions reductions from sources that have already been controlled, or methods to reduce emissions from other sources. They may also invest in energy efficiency and alternative energy. The cutting edge of protecting the environment from acid deposition will continue to develop and implement cost-effective mechanisms to cut emissions and reduce their impact on the environment.

Take action as individuals It may seem like there is not much that one individual can do to stop acid deposition. However, like many environmental problems, acid deposition is caused by the cumulative actions of millions of individual people. Therefore, each individual can also reduce their contribution to the problem and become part of the solution. One of the first steps is to understand the problem and its solutions. Individuals can contribute directly by conserving energy, since energy production causes the largest portion of the acid deposition problem. For example, you can: Turn off lights, computers, and other appliances when you're not using them Use energy efficient appliances: lighting, air conditioners, heaters, refrigerators, washing machines, etc. Only use electric appliances when you need them. Keep your thermostat at 68 F in the winter and 72 F in the summer. You can turn it even lower in the winter and higher in the summer when you are away from home. Insulate your home as best you can. Carpool, use public transportation, or better yet, walk or bicycle whenever possible Buy vehicles with low NOx emissions, and maintain all vehicles well. Be well-informed. This document is not necessarily endorsed by the Almanac of Policy Issues.

It is being preserved in the Policy Archive for historic reasons. What's Related acid rain facts, information, pictures | Encyclopedia.com articles about acid rain ACID RAIN WHAT IS ACID RAIN? Acid rain is the common name for acidic deposits that fall to Earth from the atmosphere. The term was coined in 1872 by the Scottish chemist Robert Angus Smith (1817–1884) to describe the acidic precipitation in Manchester, England . In the twenty-first century scientists study both wet and dry acidic deposits. Even though there are natural sources of acid in the atmosphere, acid rain is primarily caused by emissions of sulfur dioxide (SO2) and nitrous oxide (N2 O) from electric utilities burning fossil fuels, especially coal . These chemicals are converted to sulfuric acid and nitric acid in the atmosphere and can be carried by the winds for many miles from where the original emissions took place. (See Figure 5.1.) Other chemicals contributing to acid rain include volatile organic compounds (VOCs). These are carbon-containing chemicals that easily become vapors or gases. VOC sources include paint thinners, degreasers, and other solvents and burning fuels such as coal, natural gas, gasoline, and wood.

Wet deposition occurs when the acid falls in rain, snow, or ice. Dry deposition is caused by tiny particles (or particulates) in combustion emissions. They may stay dry as they fall or pollute cloud water and precipitation. Moist deposition occurs when the acid is trapped in cloud or fog droplets. This is most common at high altitudes and in coastal areas. Whatever its form, acid rain can create dangerously high levels of acidic impurities in water, soil, and plants. Measuring Acid Rain The acidity of any solution is measured on a potential hydrogen (pH) scale numbered from zero to fourteen, with a pH value of seven considered neutral. (See Figure 5.2.) Values higher than seven are considered more alkaline or basic (the pH of baking soda is eight); values lower than seven are considered acidic (the pH of lemon juice is two). The pH scale is a logarithmic measure. This means that every pH change of one is a tenfold change in acid content. Therefore, a decrease from pH seven to pH six is a tenfold increase in acidity; a drop from pH seven to pH five is a one hundredfold increase in acidity; and a drop from pH seven to pH four is a one thousandfold increase.

Pure, distilled water has a neutral pH of seven. Normal rainfall has a pH value of about 5.6. It is slightly acidic because it accumulates naturally occurring sulfur oxides (SOx) and nitrogen oxides (NOx) as it passes through the atmosphere. Acid rain has a pH of less than 5.6. Figure 5.3 shows the average rainfall pH measured during 2005 at various locations around the country by the National Atmospheric Deposition Program (NADP), a cooperative project between many state and federal government agencies and private entities. Rainfall was most acidic in the mid-Atlantic region and upper Southeast, particularly Ohio , Pennsylvania , West Virginia , Maryland , Delaware , Virginia, eastern Tennessee , and Kentucky . The areas with the lowest rainfall pH contain some of the country's most sensitive natural resources, such as the Appalachian Mountains, the Adirondack Mountains, Chesapeake Bay, and Great Smoky Mountains National Park. Overall, precipitation is much more acidic in the eastern United States than in the western United States because of a variety of natural and anthropogenic (human-caused) factors that are discussed below.

SOURCES OF SULFATE AND NITRATE IN THE ATMOSPHERE Natural Sources Natural sources of sulfate in the atmosphere include ocean spray, volcanic emissions, and readily oxidized hydrogen sulfide, which is released from the decomposition of organic matter found in the Earth. Natural sources of nitrogen or nitrates include NOx produced by micro-organisms in soils, by lightning during thunderstorms, FIGURE 5.1 and by forest fires. Scientists generally speculate that one-third of the sulfur and nitrogen emissions in the United States comes from these natural sources. (This is a rough estimate as there is no way to measure natural emissions as opposed to those that are manmade.) Sources Caused by Human Activity According to the U.S. Environmental Protection Agency (EPA), in "What Is Acid Rain?" (June 8, 2007, the primary anthropogenic contributors to acid rain are SO2 and NOx, resulting from the burning of fossil fuels, such as coal, oil, and natural gas. The EPA notes in "Clearinghouse for Inventories and Emissions Factors" ( that approximately 70% of SO2 emissions produced in 2006 were because of fuel combustion by fossil-fueled electric utilities.

Fuel combustion at industrial facilities contributed another 13%. Lesser sources included transportation vehicles and industrial processes. Highway vehicles were the primary source of NOx emissions, accounting for 36% of the total in 2006. Off-highway vehicles (such as bulldozers) contributed 22%. Fuel combustion in power plants was another major source, FIGURE 5.2 accounting for 20% of the total. Lesser sources included industrial processes and waste disposal and recycling NATURAL FACTORS THAT AFFECT ACID RAIN DEPOSITION Major natural factors contributing to the impact of acid rain on an area include air movement, climate, and topography and geology. Transport systems—primarily the movement of air—distribute acid emissions in definite patterns around the planet. The movement of air masses transports emitted pollutants many miles, during which the pollutants are transformed into sulfuric and nitric acid by mixing with clouds of water vapor. FIGURE 5.3 In drier climates, such as those of the western United States, windblown alkaline dust moves more freely through the air and tends to neutralize atmospheric acidity. The effects of acid rain can be greatly reduced by the presence of basic (also called alkali) substances.

Sodium, potassium, and calcium are examples of basic chemicals. When a basic and an acid chemical come into contact, they react chemically and neutralize each other. By contrast, in more humid climates where there is less dust, such as along the eastern seaboard, precipitation is more acidic. Areas most sensitive to acid rain contain hard, crystalline bedrock and thin surface soils. When no alkaline-buffering particles are in the soil, runoff from rainfall directly affects surface waters, such as mountain streams. In contrast, a thick soil covering or soil with a high buffering capacity, such as flat land, neutralizes acid rain better. Lakes tend to be most susceptible to acid rain because of low alkaline content in lake beds. A lake's depth, its watershed (the area draining into the lake), and the amount of time the water has been in the lake are also factors. EFFECTS OF ACID RAIN ON THE ENVIRONMENT In nature the combination of rain and oxides is part of a natural balance that nourishes plants and aquatic life. However, when the balance is upset by acid rain, the results to the environment can be harmful and destructive.

(See Table 5.1.) Aquatic Systems Even though pH levels vary considerably from one body of water to another, a typical pH range for the lakes and rivers in the United States is six to eight. Low pH levels kill fish, their eggs, and fish food organisms. The TABLE 5.1 Effects Recovery benefits SOURCE: "Appendix I. Effect of Acid Rain on Human Health and Selected Ecosystems and Anticipated Recovery Benefits," in Acid Rain: Emissions Trends and Effects in the Eastern United States, U.S. General Accounting Office, March 2000, (accessed July 27, 2007) Human health In the atmosphere, sulfur dioxide and nitrogen oxides become sulfate and nitrate aerosols, which increase morbidity and mortality from lung disorders, such as asthma and bronchitis, and impacts to the cardiovascular system. Decrease emergency room visits, hospital admissions, and deaths. Surface waters Acidic surface waters decrease the survivability of animal life in lakes and streams and in the more severe instances eliminate some or all types of fish and other organisms. Reduce the acidic levels of surface waters and restore animal life to the more severely damaged lakes and streams.

Forests Acid deposition contributes to forest degradation by impairing trees' growth and increasing their susceptibility to winter injury, insect infestation, and drought. It also causes leaching and depletion of natural nutrients in forest soil. Reduce stress on trees, thereby reducing the effects of winter injury, insect infestation, and drought, and reduce the leaching of soil nutrients, thereby improving overall forest health. Materials Acid deposition contributes to the corrosion and deterioration of buildings, cultural objects, and cars, which decreases their value and increases costs of correcting and repairing damage. Reduce the damage to buildings, cultural objects, and cars, and reduce the costs of correcting and repairing future damage. Visibility In the atmosphere, sulfur dioxide and nitrogen oxides form sulfate and nitrate particles, which impair visibility and affect the enjoyment of national parks and other scenic views. Extend the distance and increase the clarity at which scenery can be viewed, thus reducing limited and hazy scenes and increasing the enjoyment of national parks and other vistas. degree of damage depends on several factors, one of which is the buffering capacity of the watershed soil—the higher the alkalinity, the more slowly the lakes and streams acidify. The exposure of fish to acidified freshwater lakes and streams has been intensely studied since the 1970s.

Scientists distinguish between sudden shocks and chronic (long-term) exposure to low pH levels. Sudden, short-term shifts in pH levels result from snowmelts, which release acidic materials accumulated during the winter, or sudden rainstorms that can wash residual acid into streams and lakes. The resulting acid shock can be devastating to fish and their ecosystems. At pH levels below 4.9, fish eggs are damaged. At acid levels below 4.5, some species of fish die. Below pH 3.5, most fish die within hours. (See Table 5.2.) TABLE 5.2 Lethal to salmonids, although acclimated roach can survive for longer 3.0–3.4 Most fish are killed within hours at these levels Because many species of fish hatch in the spring, even mild increases in acidity can harm or kill the new life. Temporary increases in acidity also affect insects and other invertebrates, such as snails and crayfish, on which the fish feed. Gradual decreases of pH levels over time affect fish reproduction and spawning. Moderate levels of acidity in water can confuse a salmon's sense of smell, which it uses to find the stream from which it came.

Atlantic salmon are unable to find their home streams and rivers because of acid rain. In addition, excessive acid levels in female fish cause low amounts of calcium, thereby preventing the production of eggs. Even if eggs are produced, their development is often abnormal. Increased acidity can also cause the release of aluminum and manganese particles that are stored in a lake or river bottom. High concentrations of these metals are toxic to fish. Soil and Vegetation Acid rain is believed to harm vegetation by changing soil chemistry. Soils exposed to acid rain can gradually lose valuable nutrients, such as calcium, magnesium, and potassium and become too concentrated with dissolved inorganic aluminum, which is toxic to vegetation. Long-term changes in soil chemistry may have already affected sensitive soils, particularly in forests. Forest soils saturated in nitrogen cannot retain other nutrients required for healthy vegetation. Subsequently, these nutrients are washed away. Nutrient-poor trees are more vulnerable to climatic extremes, pest invasion, and the effects of other air pollutants, such as ozone. FIGURE 5.4 Some researchers believe that acid rain disrupts soil regeneration, which is the recycling of chemical and mineral nutrients through plants and animals back to the Earth.

They also believe acids suppress decay of organic matter, a natural process needed to enrich the soils. Valuable nutrients such as calcium and magnesium are normally bound to soil particles and are, therefore, protected from being rapidly washed into groundwater. Acid rain, however, may accelerate the process of breaking these bonds to rob the soil of these nutrients. This, in turn, decreases plant uptake of vital nutrients. (See Figure 5.4.) Acid deposition can cause leafy plants such as lettuce to hold increased amounts of potentially toxic substances such as the mineral cadmium. Research also finds a decrease in carbohydrate production in the photosynthesis process of some plants exposed to acid conditions. Research is under way to determine whether acid rain could ultimately lead to a permanent reduction in tree growth, food crop production, and soil quality. Effects on soils, forests, and crops are difficult to measure because of the many species of plants and animals, the slow rate at which ecological changes occur, and the complex interrelationships between plants and their environment. trees trees. The effect of acid rain on trees is influenced by many factors.

Some trees adapt to environmental stress better than others; the type of tree, its height, and its leaf structure (deciduous or evergreen) influence how well it will adapt to acid rain. Scientists believe that acid rain directly harms trees by leaching calcium from their foliage and indirectly harms them by lowering their tolerance to other stresses. According to the EPA, acid rain has also been implicated in impairing the winter hardening process of some trees, making them more susceptible to cold-weather damage. In some trees the roots are prone to damage because the movement of acidic rain through the soil releases aluminum ions, which are toxic to plants. One area in which acid rain has been linked to direct effects on trees is from moist deposition via acidic fogs and clouds. The concentrations of acid and SOx in fog droplets are much greater than in rainfall. In areas of frequent fog, such as London, significant damage has occurred to trees and other vegetation because the fog condenses directly on the leaves. Birds Increased freshwater acidity harms some species of migratory birds. Experts believe the dramatic decline of the North American black duck population since the 1950s is because of decreased food supplies in acidified wetlands.

Acid rain leaches calcium out of the soil and robs snails of the calcium they need to form shells. Because titmice and other species of songbirds get most of their calcium from the shells of snails, the birds are also perishing. The eggs they lay are defective—thin and fragile. The chicks either do not hatch or have bone malformations and die. In "Adverse Effects of Acid Rain on the Distribution of the Wood Thrush Hylocichla mustelina in North America " (Proceedings of the National Academy of Sciences, August 12, 2002), Ralph S. Hames et al. discuss the results of their large-scale study, which shows a clear link between acid rain and widespread population declines in the wood thrush, a type of songbird. Hames and his colleagues believe that calcium depletion has had a negative impact on this bird's food source, mainly snails, earthworms, and centipedes. The bird may also be ingesting high levels of metals that are more likely to leach out of overly acidic soils. Declining wood thrush populations are most pronounced in the higher elevations of the Adirondack, Great Smoky, and Appalachian mountains.

Hames and his cohorts warn that acid rain may also be contributing to population declines in other songbird species. Materials Acid rain can also be harmful to materials, such as building stones, marble statues, metals, and paints. Elaine McGee of the U.S. Geological Service reports in Acid Rain and Our Nation's Capital (1997, that limestone and marble are particularly vulnerable to acid rain. Historical monuments and buildings composed of these materials in the eastern United States have been hit hard by acid rain. Human Health Acid rain has several direct and indirect effects on humans. Particulates are extremely small pollutant particles that can threaten human health. Particulates related to acid rain include fine particles of SOx and nitrates. These particles can travel long distances and, when inhaled, penetrate deep into the lungs. Acid rain and the pollutants that cause it can lead to the development of bronchitis and asthma in children. Acid rain is also believed to be responsible for increasing health risks for those over the age of sixty-five; those with asthma, chronic bronchitis, and emphysema; pregnant women; and those with histories of heart disease.

THE POLITICS OF ACID RAIN Scientific research on acid rain was sporadic and largely focused on local problems until the late 1960s, when Scandinavian scientists began more systematic studies. Acid precipitation in North America was not identified until 1972, when scientists found that precipitation was acidic in eastern North America, especially in northeastern and eastern Canada . In 1975 the First International Symposium on Acid Precipitation and the Forest Ecosystem convened in Columbus, Ohio, to define the acid rain problem. Scientists used the meeting to propose a precipitation-monitoring network in the United States that would cooperate with the European and Scandinavian networks and to set up protocols for collecting and testing precipitation. In 1977 the Council on Environmental Quality was asked to develop a national acid rain research program. Several scientists drafted a report that eventually became the basis for the National Acid Precipitation Assessment Program (NAPAP). This initiative eventually translated into legislative action with the Energy Security Act of 1980. Title VII (Acid Precipitation Act of 1980) of the act produced a formal proposal that created NAPAP and authorized federally financed support.

The first international treaty aimed at limiting air pollution was the United Nations Economic Commission for Europe (UNECE) Convention on Long-Range Trans-boundary Air Pollution, which went into effect in 1983. It was ratified by thirty-eight of the fifty-four UNECE members, which included not only European countries but also Canada and the United States. The treaty targeted sulfur emissions, requiring that countries reduce emissions 30% from 1980 levels—the so-called Thirty Percent Club. The early acid rain debate centered almost exclusively on the eastern United States and Canada. The controversy was often defined as a problem of property rights. The highly valued production of electricity in coal-fired utilities in the Ohio River Valley caused acid rain to fall on land in the Northeast and Canada. An important part of the acid rain controversy in the 1980s was the adversarial relationship between U.S. and Canadian government officials over emission controls of SO2 and NO2. More of these pollutants crossed the border into Canada than the reverse. Canadian officials very quickly came to a consensus over the need for more stringent controls, whereas this consensus was lacking in the United States.

Throughout the 1980s the major lawsuits involving acid rain all came from eastern states, and the states that passed their own acid rain legislation were those in the eastern part of the United States. Legislative attempts to restrict emissions of pollutants were often defeated after strong lobbying by the coal industry and utility companies. These industries advocated further research for pollution-control technology rather than placing restrictions on utility company emissions. The NAPAP Controversy In 1980 Congress established NAPAP to study the causes and effects of acid deposition and recommend policy approaches for controlling acid rain effects. About two thousand scientists worked on this unique inter-agency program, which ultimately cost more than $500 million. Even though its first report was due in 1985, the program was plagued by problems that resulted in numerous delays. In 1985 the first executive director, Christopher Bernabo, resigned and was replaced by Lawrence Kulp. In 1987 the study group released to Congress Interim Assessment: The Causes and Effects of Acidic Deposition, a massive four-volume preliminary report that caused a storm of controversy. The report contained detailed scientific information in its technical chapters about acid rain.

The executive summary, written by Kulp, was released to the public and widely criticized for mis-representing the scientific findings of the report and downplaying the negative effects of acid rain. Philip Shabecoff notes in "Acid Rain Report Unleashes a Torrent of Controversy" (New York Times, March 20, 1990) that critics claimed Kulp had slanted the summary to match the political agenda of the administration of President Ronald Reagan (1911–2004), which advocated minimum regulation of business and industry. Some of the scientific findings in the 1987 report included: Acid rain had adversely affected aquatic life in about 10% of eastern lakes and streams. Acid rain had contributed to the decline of red spruce at high elevations by reducing this species' cold tolerance. Acid rain had contributed to erosion and corrosion of buildings and materials. Acid rain and related pollutants had reduced visibility throughout the Northeast and in parts of the West. The report concluded, however, that the incidence of serious acidification was more limited than originally feared. At that time the Adirondacks area of New York was the only region showing widespread, significant damage from acid.

Furthermore, results indicated that electricity-generating power plants were responsible for two-thirds of SO2 emissions and one-third of NOx emissions. Controversy over Kulp's role led to him being replaced by James Mulhoney. The new director ordered reassessments and revisions of the interim report. This was completed in 1991. However, by that time President George H. W. Bush (1924–) was in power, and he had made acid rain legislation a component of his election campaign. As a result, political forces, rather than NAPAP, largely drove the nation's emerging policy toward acid rain. THE ACID RAIN PROGRAM—CLEAN AIR ACT AMENDMENTS, TITLE IV Congress created the Acid Rain Program under Title IV (Acid Deposition Control) of the 1990 Clean Air Act Amendments. The goal of the program is to reduce annual emissions of SO2 and NOx from electric power plants nationwide. The program set a permanent cap on the total amount of SO2 that could be emitted by these power plants.

According to the EPA, in Acid Rain Program: 2005 Progress Report (October 2006, this cap was set at 8.9 million tons (approximately half the number of tons of SO2 emitted by these plants during 1980). The program also established NOx emissions limitations for certain coal-fired electric utility plants. The objective of these limitations was to achieve and maintain a two-million-ton reduction in NOx emission levels by 2000 compared with the emissions that would have occurred in 2000 if the limitations had not been implemented. In the 1999 Compliance Report: Acid Rain Program (July 2000, the EPA indicates that the reduction was implemented in two phases. Phase I began in 1995 and covered 263 units at 110 utility plants in 21 states with the highest levels of emissions. Most of these units were at coal-burning plants located in eastern and midwestern states. They were mandated to reduce their annual SO2 emissions by 3.5 million tons. An additional 182 units joined Phase I voluntarily, bringing the total of Phase I units to 445.

Phase II began in 2000. It tightened annual emission limits on the Phase I group and set new limits for more than two thousand cleaner and smaller units in all forty-eight contiguous states and the District of Columbia. A New Flexibility in Meeting Regulations Traditionally, environmental regulation has been achieved by the "command and control" approach, in which the regulator specifies how to reduce pollution, by what amount, and what technology to use. Title IV, however, gave utilities flexibility in choosing how to achieve these reductions. For example, utilities could reduce emissions by switching to low-sulfur coal, installing pollution-control devices called scrubbers, or shutting down plants. Utilities took advantage of their flexibility under Title IV to choose less costly ways to reduce emissions—many switching from high- to low-sulfur coal—and as a result, they have been achieving sizable reductions in their SO2 emissions. Allowance Trading Title IV also allows electric utilities to trade allowances to emit SO2. Utilities that reduce their emissions below the required levels can sell their extra allowances to other utilities to help them meet their requirements. Title IV allows companies to buy, sell, trade, and bank pollution rights. Utility units are allocated allowances based on their historic fuel consumption and a specific emissions rate.

Each allowance permits a unit to emit one ton of SO2 during or after a specific year. For each ton of SO2 discharged in a given year, one allowance is retired and can no longer be used. Companies that pollute less than the set standards will have allowances left over. They can then sell the difference to companies that pollute more than they are allowed, bringing them into compliance with overall standards. Companies that clean up their pollution would recover some of their costs by selling their pollution rights to other companies. The EPA holds an allowance auction each year. The sale offers allowances at a fixed price. This use of market-based incentives under Title IV is regarded by many as a major new method for controlling pollution. From 1995 to 1998 there was considerable buying and selling of allowances among utilities. Because the utilities that participated in Phase I reduced their sulfur emissions more than the minimum required, they did not use as many allowances as they were allocated for the first four years of the program. Those unused allowances could be used to offset SO2 emissions in future years. In Acid Rain: Emissions Trends and Effects in the Eastern United States (March 2000, the U.S. General Accounting Office (now the U.S.

Government Accountability Office) notes that from 1995 to 1998 a total of 30.2 million allowances were allocated to utilities nationwide; almost 8.7 million, FIGURE 5.5 or 29%, of the allowances were not used but were carried over (banked) for subsequent years. Figure 5.5 shows the status of the allowance bank from 1995 through 2005. Banked allowances increased dramatically in 2000 due to the addition of the Phase II sources to the Acid Rain Program. Over the next five years the allowance bank steadily decreased in size. The EPA reports in Acid Rain Program: 2005 Progress Report that in 2005 a total of 9.5 million allowances were allocated. Another 6.9 million banked allowances were carried over from previous years. The EPA expects that the allowance bank will eventually be depleted as SO2 emissions are further restricted by the implementation of the Clean Air Interstate Rule. PERFORMANCE RESULTS OF THE ACID RAIN PROGRAM There are three quantitative measures that environmental regulators use to gauge the performance of the Acid Rain Program: emissions, atmospheric concentrations, and deposition amounts. U.S.

Progress Report The following information comes from the EPA's Acid Rain Program: 2005 Progress Report. sources and emissions sources and emissions. The report notes that in 2005 there were 3,456 electric generating units subject to the SO2 provisions of the Acid Rain Program. Most emissions were associated with approximately 1,100 coal-fired units making up the total. In all, program sources emitted 10.2 million tons of SO2 into the air. (See Figure 5.6.) The EPA expects that the 8.9-million-ton annual cap on emissions will be achieved by 2010. SO2 emissions from sources covered by the program decreased by 41% between 1980 and 2005. In 2005 the NOx portion of the Acid Rain Program applied to a subset of the 3,456 units mentioned earlier, specifically 982 operating coal-fired units generating at least 25 megawatts.

Between 1990 and 2005 NOx emissions from power plants subject to the Acid Rain Program decreased from 5.5 million tons per year to 3.3 million tons per year. (See Figure 5.7.) According to the report, in 2000 the program first achieved its goal of reducing emissions by at least 2 million tons; 8.1 million tons were originally predicted in 1990 to be emitted in 2000 without the program in place. The report indicates that the SO2 and NOx emission reductions were achieved even though the amount of fuel used to produce electricity in the United States increased by more than 30% between 1990 and 2005. Coal was the FIGURE 5.6 FIGURE 5.7 single-largest fuel source for U.S. electric generating plants in 2005, accounting for 50% of the total. atmospheric concentrations and deposition amounts atmospheric concentrations and deposition amounts. The EPA's Acid Rain Program uses two complementary monitoring networks to track trends in regional air quality and acid deposition: the Clean Air Status and Trends Network and the NADP's National Trends Network.

Additional monitoring data are provided by national, state, and local ambient monitoring systems. As shown in Figure 2.14 and Figure 2.6 in Chapter 2, atmospheric levels of SO2 and NO2 averaged nationwide since 1990 have been well below the national standards for these pollutants. Table 5.3 shows trends in atmospheric concentrations and deposition for four key regions in the Acid Rain Program: mid-Atlantic, Midwest, Northeast, and Southeast. Overall, concentrations of ambient SO2 and wet sulfates averaged over the period 2003–05 declined in all these regions, compared with the period 1989–91. The most dramatic differences are evident in the Northeast, where ambient SO2 concentrations decreased by more than 50%. The results for nitrogen and nitrate compound concentrations are mixed, with decreases in some areas and increases in others. The same is true for wet inorganic nitrogen deposition, which decreased in the mid-Atlantic, Midwest, and Northeast, but increased slightly in the Southeast. Canadian Progress Report In November 2006 Environment Canada released a report on progress made by Canada and the United States on cross-border air pollution.

The study, Canada–United States Air Quality Agreement: 2006 Progress Report ( is the eighth biennial report related to the 1991 agreement between the two countries. The report states that Canada has been successful at reducing SO2 emissions below its national cap. Canada's total SO2 emissions were 2.3 million tonnes (metric tons) in 2004, which is 28% below the national cap of 3.2 million tonnes. However, Environment Canada notes that the reductions have not been sufficient to reduce acid deposition below the levels needed to ensure the recovery of ecosystems damaged by excess acidity in its eastern provinces. ARE ECOSYSTEMS RECOVERING? Monitoring data clearly indicate decreased emissions and atmospheric concentrations of SO2 and NOx and some reductions in deposition amounts. These improvements have not necessarily resulted in recovery of sensitive aquatic and terrestrial ecosystems. This is due, in part, to the long recovery times required to reverse damage done by acidification. The EPA reports that ecosystems TABLE 5.3 2.1 −5 harmed by acid rain deposition can take a long time to fully recover even after harmful emissions cease. The most chronic aquatic problems can take years to be resolved.

Forest health is even slower to improve following decreases in emissions, taking decades to recover. Finally, soil nutrient reserves (such as calcium) can take centuries to replenish. The most recent comprehensive analysis of acidified ecosystems was presented by NAPAP in the National Acid Precipitation Assessment Program Report to Congress: An Integrated Assessment (2003, The report presents a literature review summarizing findings from various government and academic studies. Overall, NAPAP finds that some ecosystems affected by acid deposition are showing limited signs of recovery. For example, one study shows that more than 25% of affected lakes and streams studied in the Adirondacks and northern Appalachians are no longer acidic. However, little to no improvement has been seen in examined water bodies in other regions, including New England and portions of Virginia. The report notes that even though chemical recovery has begun in some waterways, complete recovery for aquatic life forms, such as fish, is expected to take "significantly longer." In regards to terrestrial ecosystems, NAPAP reports that forests are under many stresses besides acid rain, such as global warming, land use changes, and air pollution from urban, agricultural, and industrial sources.

The combined effect of these stressors has greatly limited forest recovery from acidification. According to NAPAP, "There are as yet no forests in the U.S. where research indicates recovery from acid deposition is occurring." However, it is expected that reduced emissions under the Acid Rain Program will benefit forests in the long term. The report acknowledges the future benefits of continued implementation of the Acid Rain Program, but it concludes that "the emission reductions achieved by Title IV are not sufficient to allow recovery of acid-sensitive ecosystems." Recent studies support the idea that additional emission cuts 40% to 80% beyond those of the existing program will be needed to protect acid-sensitive ecosystems. NAPAP modeling indicates that even virtual elimination of SO2 emissions from power plants will be insufficient to provide this protection. It is believed that emission reductions from other sources (such as the industrial and transport sectors) will be necessary. The Next Step: The Clean Air Interstate Rule In 2005 the EPA issued the Clean Air Interstate Rule (CAIR; April 5, 2007, to address the transport of air pollutants across state lines in the eastern United States.

CAIR puts permanent caps on emissions of SO2 and NOx in twenty-eight eastern states and the District of Columbia. It is expected to reduce SO2 emissions by more than 70% and reduce NOx emissions by more than 60% compared with 2003 levels. These measures should reduce the formation of acid rain and other pollutants, such as fine particulate matter and ground-level ozone. The CAIR program will use a cap-and-trade system similar to that used in the SO2 portion of the acid rain program. The EPA projects that complete implementation of CAIR in 2015 will result in up to $100 billion in annual health benefits and a substantial reduction in premature deaths because of air pollution in the eastern United States. It should also improve visibility in southeastern national parks that have been plagued by smog in recent years. PUBLIC OPINION ABOUT ACID RAIN Every year the Gallup Organization polls Americans about their attitudes regarding environmental issues. The most recent poll to assess acid rain was conducted in March 2007.

Participants were asked to express their level of personal concern about various environmental issues, including acid rain, water pollution, soil contamination, air pollution, plant and animal extinctions, loss of tropical rain forests, damage to the ozone layer, and global warming. The results showed that acid rain ranked last among these environmental problems. Analysis of historical Gallup poll results shows a dramatic decline in concern about acid rain since the late 1980s. (See Table 5.4.) In 1989 Gallup found that 41% of respondents felt a great deal of concern about acid rain and 11% felt none at all. By 2007 only 25% of people polled were concerned a great deal about acid rain and 20% expressed no concern about the acid rain issue. TABLE 5.4 Clean Air Markets. U.S. Environmental Protection Agency. < . National Acid Precipitation Assessment Program. < National Atmospheric Deposition Program. < . Nilles, Mark A. Atmospheric Deposition Program of the U.S. Geological Survey. U.S. Geological Survey. < ACID RAIN AND THE U.S. CAPITOL BUILDING The buildings and monuments of Washington, D.C.

use many types of stone. Marble and limestone structures are the most likely to show damage caused by acid precipitation and urban pollution. They are vulnerable to accelerated deterioration because they are composed primarily of the mineral calcite (calcium carbonate), which dissolves readily in weak acid. The United States Capitol building shows evidence of stone deterioration. For example, preferential dissolution of calcite (where the silicate mineral inclusions remain) has caused pockmarks in marble columns and balustrades and their square bases. Although stone deterioration has many causes, both natural and human-induced, it is almost certain that some deterioration can be attributed to acid rain. Cite this article Acid Rain - NYS Dept. of Environmental Conservation Acid Rain Click to see large image Acid rain comes in many forms: rain, snow, sleet, hail and fog (wet deposition), and as deposits of acid particles, aerosols and gases (dry deposition). It is formed when sulfur dioxide (SO2) and nitrogen oxides (NOx) combine with moisture in the atmosphere to produce sulfuric acid and nitric acid.

Causes of Acid Rain Several sources that contribute to creating acid rain include: Combustion of fossil fuels (coal, oil, natural gas, wood, etc.) for energy. Emissions from motor vehicles, airplanes, power plants and industries. Emissions of SO2 and NOx from the Midwest. Effects of Acid Rain on the Environment Aquatic - Freshwater macroinvertebrates , plants, and fish populations are damaged when acidic water disrupts their reproductive cycle. Aluminum leaches from the soil into the water, altering the chemistry and clogging the fish's gills. As water bodies become acidified, one species after another disappears. In addition to sensitive lakes, the Adirondack region includes thousands of miles of streams and rivers that are also sensitive to acidic deposition. Wildlife - Acid rain lowers the biological productivity of lakes and reduces the amount of forage fish available to loons. Toxicity from mercury pollution of water bodies can lead to decreased reproductive success of loons as well. Forests - Sulfur and nitrogen deposition have caused adverse impacts on certain highly-sensitive forest ecosystems, most notably the high-elevation, spruce-fir forests in the eastern United States. Forests are damaged because acid precipitation drains nutrients from the soil.

Excess nitrogen in the air also may adversely affect tree growth. Evidence of decreased growth and dieback has been found in the Adirondacks. Visibility - Dry acidic particles in the air lessen visibility. When winds blow from the southwest at Whiteface Mountain in the Adirondacks, visibility can be reduced from 50 miles to fewer than 5 miles. Architecture - For materials, buildings, bridges and cultural resources, dry deposition is now considered to be more damaging to stone than wet deposition. Human Health - High concentrations of fine-particulate sulfate and nitrate can enter the cardiovascular and respiratory systems, resulting in disease or even death. Metals, such as mercury and cadmium from soil deposits in lakes, streams, and reservoirs, can accumulate in the tissues of fish, making them toxic to humans. Metals also can be leached from the soil into reservoirs, or from old lead and copper pipes directly into home water supplies, causing serious illness. Things You Can Do to Help Conserve energy in your home and office. Utilize public transportation, car pool, or walk. Purchase clean electric power. Learn more about acid rain on EPA's Acid Rain information webpage.

More about Acid Rain: Acid Deposition - Shenandoah National Park (U.S. National Park Service) Acid Deposition Schematic of acid deposition sources, transport, and receipt. EPA Acid Rain website What is Acid Rain and What Causes It? Scientists discovered and have confirmed, that sulfur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acidic conditions in the atmosphere. In the United States, about 2/3 of all SO2 and 1/4 of all NOx comes from electric power generation that relies on burning fossil fuels like coal (EPA Acid Rain website). Acidic conditions develop when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of most of these reactions. The result is a mild solution of sulfuric acid and nitric acid. The acidic compounds then fall to or are deposited on the earth’s surface. "Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. Acid rain is usually used in reference to rain, snow, sleet, and hail.

A more precise term is acid deposition, which includes all forms of precipitation but also includes deposition of dry particles and gases as well as occult or cloud, fog water, and rime ice deposition. Rime ice is most frequently found in the freezer compartment of a refrigerator but under certain conditions also occurs naturally outside. Thus, acid deposition has three components: wet, dry and occult deposition. Occult deposition is very difficult and expensive to measure. However, in the few places where occult deposition has been monitored, it typically has much higher concentrations of acidic compounds than either wet or dry deposition. Dry deposited gases and particles fall onto buildings, cars, homes, trees, and the ground. They can be washed from trees and other surfaces by rainstorms. When that happens, the dry deposition adds to the acids in the precipitation, making runoff even more acidic. Acidic water flows over and through the ground, affecting soil and water chemistry and a variety of plants and animals. The strength of the effects depend on many factors, including how acidic the water is, the chemistry and buffering capacity of the soils and surface waters involved, and the types of fish, trees, and other living things that rely on the water.

Prevailing winds blow the compounds that contribute to acid deposition across state and national borders, and sometimes over hundreds of miles. Normally rain water is slightly acidic, with a pH of between 4.9 and 6.0, because in the atmosphere, water reacts with carbon dioxide to form a weak carbonic acid. Pure water would have a neutral pH of 7. It is important to point out that the “normal” range cited here must be evaluated in the context of site-specific circumstances and acid conditions. In certain situations, even slight changes in acidity can have serious environmental consequences. Effects of Acid Deposition Acid rain causes acidification of lakes, streams, and sensitive forest soils and can damage trees and other plants. The presence of sulfur on and in the soil and water releases aluminum, making it available to plants, soil microbes, fish and other organisms. Acid particles also alter the nutrient make-up of forest soils. This chemical alteration may, at first, result in fertilization which can cause changes in plant growth, species composition, and pathogen development. A pathogen is a plant or animal that is capable of producing disease. Eventually, however, the soil becomes acidified.

This can result in impairment of plant growth and development because nutrients that would otherwise be available to plants are diminished. These chemical alterations are particularly acute at high elevation sites because nitrogen is limited in those soils to begin with. Nutrient deficiency can lead to susceptibility to disease. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation's cultural heritage. Acid Deposition at Shenandoah Acid deposition is a particular concern at Shenandoah National Park for several reasons. First, acid deposition levels occurring within the park are amongst the highest when compared to other parks that collect deposition information. Second, roughly 60% of the watersheds within the park include bedrock types that have a low acid buffering capacity. This allows chemical interactions between soil, bedrock, and surface waters with acid depositions to proceed without neutralization or buffering. Third, streams within the park provide important habitat to fish and other aquatic organisms that are particularly sensitive to the acidic condition of the water in which they live. Fourth, forested areas within the park are subjected to various forms of stress including drought, disease, and insect damage.

In some cases, the diseases and insects are not native to the park. Acid deposition builds on these conditions causing direct and indirect damage to forest vegetation. Park staff members are working to improve the situation by monitoring acid deposition conditions, by supporting research to better understand the effects of deposition and predict the consequences, as well as by working on reducing emissions both inside and outside of the park. To read a fact sheet on this topic click here . Related Information Helpful literature related to acid deposition includes: Driscoll, C.T., G.B.Lawrence, A.J. Bulger, T.J. Butler, C.S. Cronan, C. Eagar, K.F. Lambert, G.E. Likens, J.L. Stoddard, K.C. Weathers, 2001. Acid Rain Revisited: Advances in scientific understanding since the passage of the 1970 and 1990 Clean Air Act Amendments. Hubbard Brook Research Foundation. Science LinksTM Publication. Vol. 1, no. 1. Driscoll, C.T. 2003. Nitrogen Pollution: From the Sources to the Sea. Hubbard Brook Research Foundation. Science LinksTM Publication. Vol.

1, no. 2. Garner, J.H.B., T. Pagano, and E.B. Cowling. 1989. An evaluation of the role of ozone, acid deposition, and other airborne pollutants in the forests of eastern North America

Question: When acid rain is caused by power generation plants, normally what acid does it contain?
Answer: Nitric acid