These boilers contributed over 60 percent of all utility emissions of SO2 in 1980. Sulfur dioxide is a by-product of burning coal and oil that reacts with other substances in the atmosphere to form acidic compounds that are carried down to ground level in rain, snow and dust.
People suffering from asthma and other lung ailments are especially vulnerable to airborne sulfates.
Acid rain also harms fish and lakes, damages high-altitude forests and contributes to the deterioration of buildings. The 445 electric utility boilers in the program in 1995, among the nation's largest and highest emitting facilities, produced only 5.3 million tons of SO2 last year compared to their 1980 levels of 10.9 million tons. Coupled with the emission reductions from other industrial and transportation sources, total national SO2 emissions have declined from 25.9 million tons in 1980 to 18.0 million tons in 1995. Most of that reduction has taken place since 1993. The remaining 1500 boilers in the United States are required to control emissions by 2010 beginning in 2000.