Acid Rain - Emissions And Deposition
program million so2 tons
Each year the EPA publishes a report detailing the progress achieved by the Acid Rain Program. The latest report is titled Acid Rain Program, 2002 Progress Report and was published in November 2003.
The report notes that in 2002 there were 3,208 electric generating units subject to the SO2 provisions of the Acid Rain Program. They emitted 10.2 million tons of SO2 into the air as shown in Figure 7.7. The EPA expects that the 8.95-million-ton annual cap will be achieved by the year 2010. SO2 emissions from sources covered by the program decreased by 41 percent between 1980 and 2002.
The downward trend in SO2 emissions was accompanied by a decrease in SO2 concentrations measured in the air and in sulfate deposition recorded at monitoring sites operated by the National Atmospheric Deposition Program. Between 1990 and 2002 average SO2 concentrations in the atmosphere decreased by 54 percent. Wet sulfate deposition across the Northeast and Midwest declined by approximately 50 percent.
Between 1990 and 2002 NO5 emissions from power plants subject to the Acid Rain Program decreased from 6.7 million tons per year to 4.5 million tons per year. In 2000 the program achieved its goal of reducing emissions by at least two million tons; 8.1 million tons were originally predicted in 1990 to be emitted in the year 2000 without the program in place.
Decreased NO5 emissions have not resulted in uniformly lower levels of NO5 in the atmosphere or in deposits measured at recording stations. The EPA reports that concentrations of wet nitrates in the atmosphere generally remained constant between 1989 and 2002 across much of the country. In a few areas, concentrations actually increased. Progress for wet nitrate deposition was a little more promising. Large decreases in deposition were reported across the Northeast and the state of Michigan. Unfortunately, most of the Midwest and the mid-Atlantic regions showed little to no significant improvement.