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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. © Illinois EPA

August 2007 Big changes in a big hurry Wisconsin industries became early adopters, cut acid rain, and got way ahead on the environmental and economic curve. Could the approach help us today? Anne Urbanski

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:

• Reduced acid rain and kept the pH of precipitation more neutral (at least 4.7) across Wisconsin.
  
  
• Created standards for nitrogen oxide and sulfur dioxide emissions from different sources.
  
  
• Required the state's five major electric utilities to reduce their sulfur dioxide emissions to 50 percent of 1980 levels by 1993.
  
  
• Capped annual emissions from the state's five major electric utilities at 250,000 tons of sulfur dioxide beginning in 1993, and 135,000 tons of nitrogen oxides beginning in 1991.
  
  
• Kept sulfur dioxide emissions from all large sources in Wisconsin below 75,000 tons per year.
  
  
• Reduced average sulfur dioxide emissions to 1.5 pounds per million BTUs of heat produced by plants owned by Wisconsin companies.

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.