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In the late 1970s acid rain started making worldwide news, thanks to research showing that acidic rainfall was damaging lakes, fisheries and forests in Europe and Canada. DNR research teams in 1979 tested lakes around Wisconsin and concluded that half of the northern lakes tested were vulnerable to damage from acid rain. Researchers found that these acidity levels were damaging fish, forests, crops and even stone monuments around the state. The data raised an alarm heard across the state and eventually led the Wisconsin Legislature to enact one of the first and strongest acid rain laws in the nation.
Acid rain is caused primarily by emissions of sulfur dioxide and nitrogen oxides. Sulfur dioxide emissions come mostly from coal-fired power plants and pulp and paper mills. Nitrogen oxide emissions come mostly from coal-fired power plants, factories, motor vehicles and home furnaces. While in the air, sulfur dioxide and nitrogen oxides react with oxygen and moisture to form sulfuric acid, nitric acid and nitrous acid, which return to the land as precipitation through rain, snow or fog.
Wisconsin's acid rain law aimed to reverse the damage resulting from acid rain by aggressively limiting emissions of nitrogen oxides beginning in 1991 and sulfur dioxide beginning in 1993. The law passed in April 1986 and these goals were met:
In just a few years, compliance with the state law brought noticeable improvements to Wisconsin's air and waters. By l990 sulfur dioxide emissions from electric utilities had already fallen 46 percent. By 1992 these companies projected they would easily meet the law's mandates. During the subsequent 20 years, these changes at electric utilities helped reduce sulfur dioxide emissions by two-thirds compared to 1980 levels and improved the pH range to 4.78 in southeastern lakes and 5.29 in northwestern lakes.
Anne Urbanski communicates about emerging air issues, public health and policy for DNR's Air Management program.