Photograph by Oxford Scientific/Photolibrary
Coal-fired power plants and other fossil-fuel combustion emit chemicals that react with water and oxygen in the air to produce nitric and sulfuric acids. These acids fall back to earth, over time changing the chemistry of lakes and forest soils, damaging trees and wearing down roads and bridges.
President George H.W. Bush campaigned to be the "environmental president," and his signature on the Clean Air Act Amendments of 1990 created the most important environmental law since the 1970s. The "cap and trade" program set up by the law puts limits on air pollution and allows companies to buy and sell emissions permits. The program reduced pollution faster and at a lower cost than expected, according to the EPA.
Pictured: Spruce trees killed by acid rain in Krkonose National Park in the Czech Republic.
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