Acid Rain

Emissions Trends and Effects in the Eastern United States Gao ID: RCED-00-47 March 9, 2000

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.

GAO noted that: (1) in the United States, total emissions of sulfur dioxide declined 17 percent from 1990 through 1998, but total emissions of nitrogen oxides changed little during the same time period; (2) sulfur dioxide emissions from electric utility power plants also declined 17 percent during this period, and nitrogen oxide emissions from electric utility power plants declined by 8 percent; (3) in the eastern United States, total deposition of sulfur decreased 26 percent from 1989 through 1998, while total deposition of nitrogen decreased 2 percent, according to a preliminary analysis performed by an Environmental Protection Agency (EPA) contractor of data collected by EPA and other federal agencies; (4) for the three environmentally sensitive areas, the trends were generally similar; (5) there was a 26 percent decrease in wet sulfate deposition in the Adirondack Mountains; (6) in the Adirondack Mountains from 1992 through 1999, sulfates declined in 92 percent of a representative sample of lakes, but nitrates increased in 48 percent of those lakes; (7) the decrease in sulfates is consistent with decreases in sulfur emissions and deposition, but the increase in nitrates is inconsistent with the stable levels of nitrogen emissions and deposition; (8) on the basis of GAO's review of relevant scientific literature, it appears that the vegetation and land surrounding these lakes have lost some of their previous capacity to use nitrogen, which allowed more of the nitrogen to flow into the lakes and increase their acidity; (9) increases in these lakes' acidity raise questions about their prospects for recovering under the current program and being able to support fish and other wildlife; (10) the utilities in the 11 midwestern states relied on sulfur dioxide allowances that originated in those states for 11.2 million of the 13.9 million allowances they used from 1995 through 1998, according to EPA's data; and (11) conversely, the utilities used 2.7 million allowances that originated in other states, of which about 538,000 originated in six northeastern and mid-Atlantic states.

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