Sour Showers; September 2010; Scientific American Magazine; by Michael Tennesen; 2 Page(s)

The acid rain scourge of the 1970s and 1980s that killed trees and fish and even dissolved statues on Washington, D.C.’s National Mall has returned with a twist. Rather than being sulfuric acid derived from industrial sulfur emissions, the corrosive liquid is nitric acid, which has resulted not just from smokestacks but also from farming.

Besides dissolving cement and limestone and lowering the pH of lakes and streams, acid rain leaches critical soil nutrients, injuring plants, and liberates toxic minerals that can enter aquatic habitats. To combat the problem the first time around, the U.S. Environmental Protection Agency passed the Clean Air Act Amendments of 1990, which cut sulfur emissions from power plants by 59 percent from 1990 to 2008. Emissions of nitrogen compounds, however, have not fallen as steeply.