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Environmental Benefits of Reducing Acid Rain

The Clean Air Act Amendments of 1990 call for major reductions in the pollutants that cause acid rain. The Amendments also establish a new approach to environmental management. By the year 2010, the Acid Rain Program will result in a 10-million-ton reduction in sulfur dioxide emissions from 1980 levels. This page answers some of the most commonly asked questions about the environmental benefits of the Acid Rain Program.



What is acid rain?
Acid rain is caused when sulfur dioxide and nitrogen oxides -- pollutants released primarily from the burning of coal, oil, and other fossil fuels -- chemically react with other substances in the atmosphere to form acidic compounds. When these acidic compounds are carried down from the atmosphere in rain, fog, snow, or dust, they can end up in lakes and streams, on buildings and monuments, or on trees and land. They can harm fish, damage high-altitude forests, and contribute to the deterioration of buildings and historical monuments. The pollutants that cause acid rain also have been known to worsen asthma and other lung ailments and to impair visibility in many regions of the nation, including the scenic vistas of our national parks.

How does acid rain affect lakes and streams?
When acid rain passes through soils or falls directly into our lakes and streams, it can increase the acidity of the water, a process called acidification. Increases in water acidity can impair the ability of certain types of fish and water plants to reproduce, grow, and survive. In some acidified lakes and streams, entire fish populations have disappeared, leaving the bodies of water barren. For example, many lakes in the Adirondack Mountains of New York and many streams in the Appalachian mountain region have experienced losses of trout and other aquatic life due to acid rain.

The effects of acid rain can be either "chronic" or "episodic." Chronic acidity occurs when lakes and streams cannot counteract the chemical changes brought about by acid rain. This results in constant high acidity levels in the water. Episodic acidity occurs only periodically, primarily as a result of storms or snowmelts that empty large amounts of acidic water into lakes and streams. In the case of episodic acidity, lakes and streams suffer from intense but short-lived increases in acidity. In the spring, when such episodes often occur, newly hatched fish can be killed.

Some lakes and streams are naturally more sensitive to acid rain because they rest in soil that cannot neutralize acids. In the mid-1980's, the U.S. Environmental Protection Agency (EPA) and other federal agencies commissioned a National Surface Water Survey to examine the effect of acid rain in over 1,000 lakes and thousands of miles of streams. From this survey, it was determined that of the water bodies found to be acidic, acid rain was the primary cause of the acidity. While the acidity of some lakes and streams can be attributed to natural causes, most cases of acidity in the United States result from acid rain.

Where are the acidified lakes and streams located?
According to the National Surface Water Survey, about 14 percent of the lakes (larger than 10 acres) in the Adirondack Mountains in New York are chronically acidic, as are about 12 percent of streams in the mid-Atlantic Highlands (which include southeastern New York, most of Pennsylvania, and portions of Maryland, West Virginia, and Virginia) and the mid-Appalachians (which include Virginia, West Virginia, Maryland, Pennsylvania, and North Carolina). Other affected areas include Florida and the Upper Peninsula of Michigan. In addition, many lakes and streams throughout the United States, including those in the West, are sensitive to episodic acidification. The Canadian government has estimated that 14,000 lakes in eastern Canada are acidic, in part because of sulfur dioxide emissions from U.S. utilities and industrial plants.

How does acid rain harm forests?
Acid rain can contribute to forest damage by impairing the ability of some types of trees to grow and fight disease. Acid rain also can strip forest soils of essential nutrients, which hurts the productivity of forests.

Which forest regions are most affected by acid rain?
Acid rain has primarily impacted high-elevation spruce trees that grow on the ridges of the Appalachian Mountains from Maine to Georgia, including spruce trees in the Shenandoah National Park and the Great Smokey Mountains National Park.

How does acid rain affect visibility?
The chemical reactions that sulfur dioxide and nitrogen oxides undergo in the atmosphere lead to the formation of particles that can reduce the distance we see and the clarity of our scenic vistas. These particles account for over 50 percent of the visibility problems in the eastern United States. In the West, such particles also have been blamed for visibility problems in the Grand Canyon and other national parks in the Colorado River Plateau.

Does acid rain contribute to the decay of buildings and monuments?
Acid rain is known to contribute to the corrosion of metals and to the deterioration and soiling of stone and paint on buildings, statues, and other structures of cultural significance. The damage inflicted on cultural objects is especially costly since a loss of detail caused by the destructive potential of acid rain seriously depreciates the objects' value to society.

Is acid rain detrimental to public health?
High levels of sulfur dioxide in the air have been proven to cause and aggravate various types of lung disorders. These lung disorders, which affect some people's ability to breathe, have led to both increased disease rates and mortality in sensitive populations, such as young children and the elderly. Low levels of acidic compounds and acid aerosols commonly found in the air in the eastern United States can also pose health problems, and EPA has been asked by a panel of outside experts to investigate this issue.

What are the benefits of acid rain legislation?
The substantial reductions in sulfur dioxide and nitrogen oxides emissions that will take place because of the Act will help improve environmental and health conditions in the United States. In particular, scientists have projected that emissions reductions will increase the visual range in the eastern United States by 30 percent and reduce the deterioration of buildings and monuments. In addition, scientists predict that the Acid Rain Program will virtually eliminate acidity in the lakes and streams of the Adirondacks caused by sulfur dioxide emissions and help bodies of water and forests throughout the United States recover from the effects of acid rain.

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