Although mobile sources like cars and trucks contribute to our Nation's pollution problems, much of our air, land, and water pollution come from stationary sources, such as power plants, oil refineries, and industries that manufacture steel, textiles, and pesticides. Today there are more than 20,000 major stationary sources in the United States and hundreds of thousands of lesser ones, including home and commercial furnaces. These sources are a primary cause of the environmental problems identified by the U.S. Environmental Protection Agency (EPA) as having 'potential for widespread adverse effects on human health and welfare'. The combustion of fossil fuels (coal, oil, and natural gas) causes a large part of the pollution from stationary sources. As supplies of oil and natural gas dwindle, more power plants and industries will convert to coal, a 'dirtier' fuel that emits significantly more of most major pollutants. As a result, pollution from stationary sources will increase in the years ahead unless we do something about it now.