emitted from automobiles and industrial smokestacks (Babich, Davis, & Stotzky, 1980, pp. 6-8).
In 1980, the United States attributed 65 percent of its acid deposition to sulfuric acid, 30 percent to nitric acid and 5 percent to hydrochloric acid. The world sulfur dioxide emission amounted to more than 200 tons annually. The growing use of coal to produce energy is resulting in a further increase of the world's sulfur emissions (Izrael, 1983, pp. 1-10). Only 7 percent of sulfur dioxides in the atmosphere come from natural sources, such as sea spray and volcanoes, about 93 percent come from man-made sources.
As these pollutants move through the atmosphere, sulfur dioxide and nitrogen oxide are changed into sulfuric and nitric acids through the process of oxidation. The longer sulfur dioxide and nitrogen oxide remain in the atmosphere, the greater the probability they will oxidize and become acids. These acids eventually find their way back to the earth in the form of rain, precipitation, or solid deposits.
This transfer of acidic gases or particles from the air to the ground takes place by "wet" and "dry" means. Wet deposition includes all gases, liquids or solids removed from the atmosphere by rain and other forms of precipitation. This precipitation is usually deposited far away from the original source of pollution. Dry deposition includes all materials transferred from the atmosphere to the ground by means other than precipitation. These materials are usually deposited near the original pollution source ("Committee," 1984, pp. 55-65).
The acidity of these deposits is determined by the presence of free hydrogen ions. The scientific measurement of hydrocarbon ion concentration is a 14-point logarithmic scale of pH values, with 0 to 7 the acidic range and 7 to 14 the alkaline range. Normal, unpolluted water is slightly acidic, falling within the 5.6 to 7 range. Acid precipitation has a pH level of 2 to 5, with...