Formed by combustion of fuels containing sulfur--primarily coal and oil. Major health effects associated with SO2 include asthma, respiratory illness, and aggravation of existing cardiovascular disease. SO2 combines with water and oxygen in the atmosphere to form acid rain, which raises the acid levels of lakes and streams, affecting the ability of fish and some amphibians to survive. It also damages sensitive forests and ecosystems, particularly in the eastern part of the U.S. It also accelerates the decay of buildings. Making electricity is responsible for two-thirds of all the SO2 pollution in the U.S., 13 million tons each year.