Vehicles Are Not the Cause of Most Acid Rain

An important component of acid rain in the Northeastern and Midwestern United States comes primarily from coal-fired power plants and industry hundreds of miles upwind, according to a new U.S. Geologic Survey analysis.

The Clean Air Act amendments of 1990 worked effectively to drive down concentrations of sulphuric acid found in mountain streams, but the levels of nitrate were less responsive. Since industry was reducing both acid gases, some hypothesized that automobiles were a primary driver of ongoing acid rain.

"Although vehicles are the single largest emission source of nitrogen oxides in this region, distant stationary sources may have a greater impact on nitrate found in rain and snow," reads a USGS press release on the subject. The new study is published in the journal Environmental Science and Technology.

Nitrogen and sulphur oxides are created by burning fossil fuels. The tall smokestacks of many power plants put these acid gases high in the atmosphere, where they are transported hundreds of miles before raining down, or being deposited as mist or dust. The ongoing rain of these acids has caused many streams and lakes in Northeastern mountains -- including the Adirondacks of New York -- to become so acidic they can no longer support life. Even after the largely successful cap-and-trade program for acid gases instituted by the 1990 Clean Air Act amendments, many water bodies have been surprisingly slow to recover because the acid rain did such lasting damage to the soil, debilitating its ability to buffer even small amounts of acid before it reaches the water.

The scientists still believe vehicles are an important source of nitrogen oxides, but because their tailpipes are near to the ground, their effect is believed to be local, whereas the tall smokestacks of Midwestern power plants spit pollutants high into the atmosphere.

Nitrogen oxides also contribute to ozone pollution, a major component of smog. This pollutant irritates the lungs and may do lasting damage to the respiratory and circulatory system.

New Environmental Protection Agency regulations are going into effect to reduce emissions of nitrogen oxides, and recent court settlements dating to Clinton Administration prosecutions -- including a record $4.6 billion settlement with AEP earlier this month -- are working to reduce these emissions from coal-fired power plants.

To read more, see this abstract of the research.

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