Summary: In 1990, Congress directed the Environmental Protection Agency (EPA) to reduce sulfur dioxide and nitrogen oxide emissions from electric utility power plants. These two emissions are major contributors to acid rain. GAO found that in the first four years of the Acid Rain Program (1995 through 1998), sulfur dioxide emissions generally continued their long-term decline, while nitrogen oxide levels remained stable. Sulfate deposition in the eastern states and in three environmentally sensitive areas--the Adirondack Mountains, the mid-Appalachian region, and the southern Blue Ridge area--also declined, as did the level of sulfates in a sample of lakes in the Adirondack Mountains. However, the level of nitrates in these lakes often rose, apparently because the vegetation and soils surrounding the lakes have lost some of their capacity to use nitrogen. These trends underscore the significance of nitrogen oxide emissions and the resulting nitrogen deposition, which may not have been fully appreciated when the 1990 law was being drafted. Because the law requires relatively little reduction in nitrogen oxide emissions, the prospects are uncertain for the recovery of already acidified lakes and for preventing further acidification.
