According to the federal National Acid Precipitation Assessment Program, acid rain is the result of a series of complex reactions involving chemicals and compounds from many industrial, transportation, and natural sources. As a result, SO 2 emissions have dropped even though coal use has increased. All ranks of coal have some value or use. For centuries peat has been used as a fuel for open fires, and more recently peat and lignite have been made into briquettes for burning in furnaces. Electric utilities use about 86 percent of all the bituminous coal consumed in the United States.
General industry is the second largest consumer.
Steel producers use metallurgical coal, or coke , a distilled fuel that is almost pure carbon. The process of producing coke yields a number of chemical by-products, including coal tar , which are used in the manufacture of many other products. Manufacture of fuel gas and other products from coal diminished as natural gas became widely available. Coal liquefaction supplies all of the Republic of South Africa's oil needs.