Air pollution is a general term that covers a broad range of contaminants in the atmosphere. Pollution can occur from natural causes or from human activities. Discussions about the effects of air pollution have focused mainly on human health but attention is being directed to environmental quality and amenity as well. Air pollutants are found as gases or particles, and on a restricted scale they can be trapped inside buildings as indoor air pollutants. Urban air pollution has long been an important concern for civic administrators, but increasingly, air pollution has become an international problem.

The most characteristic sources of air pollution have always been combustion processes. Here the most obvious pollutant is smoke. However, the widespread use of fossil fuels have made sulfur and nitrogen oxides pollutants of great concern. With increasing use of petroleum-based fuels, a range of organic compounds have become widespread in...