Many sources of air pollution are man-made. Industrial processes often create both types of pollutants that escape into the air. Automobiles and other moving sources of pollution affect the quality of air. Agriculture adds to air pollution through the methane and ammonia produced by animal waste. Improper application of agricultural chemicals also increases the pollution in the air.
Some natural sources add to air pollution levels. Volcanic eruptions, thunderstorms and forest fires are causes of air pollution. These sources add toxic and particulate matter to the air. Natural pollution is often more difficult to control than man-made sources, but the EPA indicates that man-made sources are the major source of pollutants.
In the United States, the Clean Air Act governs many of the sources of man-made pollutants. Several chemicals regulated under this act cause cancer or an increase in birth defects. Others cause ecological or environmental concerns.