Acid Rain Active

BACKGROUND

Acid rain is the term commonly used by scientists to describe rain that is abnormally acidic. What does that mean? Well, plain distilled water, like that used in laboratories, is neutral (not acidic or basic). Since rain naturally has things dissolved in it, it will always be slightly acidic. However, when rain reacts with certain air pollutants, such as sulfur or nitrogen oxides, the water vapor converts into very diluted forms of sulfuric or nitric acids. The acidity of this rain is on par with that of grapefruit juice, which may not seem like much, but is much more caustic than plain water.

The main sources of pollutants that trigger acid rain are vehicles and industrial and power-generating plants. The areas of greatest acidity are 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.

IMPACT OF ACID RAIN ON FORESTS

Acid rain can dissolve certain more soluble elements from the soil, like aluminum. The dissolved aluminum begins to accumulate and can reach toxic levels as it enters local streams and wetlands. Acid rain also removes important nutrients from the soil, such as calcium, potassium, and magnesium. The lack of nutrients can negatively affect the health of plants and animals. Lastly, the combination of reduced calcium and excessive aluminum can make forests more susceptible to pests, disease, and injury from freezing and drought, as a proper balance of these nutrients is vital to forest health.

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WHAT USGS AND OTHERS DOING ABOUT ACID RAIN?

Scientists from many disciplines study acid rain and its impact. The National Acid Precipitation Assessment Program (NAPAP), a Federal program involving representatives from more than a dozen Federal agencies, has sponsored studies on how acid rain forms and how it affects lakes, crops, forests, and materials. Because buildings and monuments cannot adapt to changes in the environment, as plants and animals can, historic structures may be particularly affected by acid precipitation. Scientists are studying effective control technologies to limit the emissions from power plants and automobiles that cause acid rain. The impact and usefulness of regulations that would require limits on air pollution are also being studied. Finally, scientists are examining the processes of deterioration to find effective ways to protect and repair our historic buildings and monuments. Agencies like the National Park Service, which are charged with protecting and preserving our national heritage, are particularly concerned not only about the impact of acid rain but also about making the best choices for maintaining and preserving our historic buildings and monuments.

RELATED USGS RESEARCH

The USGS investigates the chemistry, source, fate, and transport of airborne pollutants and their affect on the landscape.

• Acid Rain, Atmospheric Deposition and Precipitation Chemistry
• Acid Rain: Do you need to start wearing a rain hat?
• Acid Rain and Our Nation's Capital

ADDITIONAL RESOURCES

National Atmospheric Deposition Program

U.S. Environmental Protection Agency

• Acid Rain
• What is Acid Rain?
• Effects of Acid Rain
• Clean Air Markets