Clean air act and acid precipitation receiving increased attention

Abstract

In 1990 the U.S. Congress passed Title IV of the Clean Air Act Amendments, which was intended to reduce the adverse effects of acid deposition by reducing emissions of the acid precursors,sulfur dioxide (SO2) and nitrogen oxides (Nox). Passage of Title IV was a response to the findings of a decade of research performed in large part through the National Acid Precipitation Assessment Program (NAPAP), which concluded that acid deposition posed a current and future threat to vulnerable forest and aquatic ecosystems [NAPAP, 1991].Now,with reauthorization of the 1990 Clean Air Act Amendments scheduled for 2000, Congress is considering several bills that would further reduce emissions to ensure the restoration of damaged ecosystems.Title IV requires a 10 million ton per year reduction in SO2 emissions below 1980 levels by 2010 and establishes a national cap of 8.95 million tons per year on utility emissions by 2010. Atmospheric sulfur deposition began to decline in the late 1970s as a result of energy conservation and provisions of the Clean Air Act of 1980. Since implementation of Phase I of Title IV in 1995, SO2 emissions have dropped from more than 20 million tons per year in the early 1990s to 18.3 million tons in 1995 [NAPAP, 1998].Consequently, reductions in atmospheric sulfur deposition have accelerated throughout the United States since 1995.