Air pollution

Air pollution is a chemical, physical (e.g. particulate matter), or biological agent that modifies the normal characteristics of the atmosphere. Stratospheric ozone depletion due to air pollution has long been known as a threat to human health as well as to the earth's ecosystems.
Worldwide air pollution is in charge for large numbers of deaths and cases of respiratory disease. Enforced air quality standards, like the Clean Air Act in the United States, have reduced the occurrence of some pollutants. While major stationary sources are often identified with air pollution, the greatest source of emissions are in fact mobile sources, principally the automobile. Gases such as carbon dioxide, which contribute to global warming, have newly gained recognition as pollutants.