Sulfur Dioxide

Sulfur dioxide is a gas released into the atmosphere during the combustion of fossil fuels that contain sulfur. In the atmosphere, sulfur dioxide is transformed into sulfates, which are secondary pollutants. Sulfates are main contributors to visibility reduction and acid deposition in the southern Appalachians (SAMAB 1996).

Trends in primary pollutants in the
southern Appalachians from 1940-1995

Coal-fired electricity generating plants are major sources of sulfur-dioxide emissions nationally. Many of these are located inside the southern Appalachian region in northern Alabama, northern Georgia, and eastern Tennessee. Other large sources near the region are on the Piedmont Plateau in North Carolina, in the Ohio Valley, and on the Allegheny Plateau in West Virginia and Pennsylvania. These large sulfur dioxide sources contribute to impacts in portions of the southern Appalachians because emissions are transported and changed to sulfates downwind of the facilities. The Copper Hill area in eastern Tennessee is a notable example. This area experienced a century of uncontrolled emissions of sulfur dioxide from crude copper-smelting operations. Emissions so large that they were toxic to vegetation severely affected approximately 32,000 acres of the basin. This damage could still be seen 50 years later when the Tennessee Valley Authority began reclamation work (SAMAB 1996).

In the nation as a whole, sulfur dioxide emissions increased between 1940 and 1970 and since then have steadily decreased to approximately 1940 levels (see figure at right). Despite this national decrease, the EPA has reported sulfur dioxide emissions in EPA Regions III and IV, which include the Southern Appalachian Assessment, have increased slightly between 1985 and 1994 (EPA 1995). The 1990 Clean Air Act Amendments will reduce sulfur dioxide emissions by 10 million tons below the 1980 level, and there will be a cap on emissions from utility and industrial sources. Emissions are expected to decrease in the southern Appalachians, but the full extent of reduction is uncertain, because sulfur dioxide sources within and near the assessment area can achieve these emission reductions by purchasing credits from sources in other regions of the United States (SAMAB 1996).