US Environmental Protection Agency
Epa: Criteria Air Pollutants
Find out about the six major air pollutants. In-depth descriptions of ozone, nitrogen dioxide, particulates, sulfur dioxide, carbon monoxide, and lead are provided.
Encyclopedia of Earth
Encyclopedia of Earth: Air Pollution Emissions
Explains what air pollution is, countries with the worst occurrences of it, the history of air pollution, how air pollutants are dispersed and how scientists study this phenomenon, sources of air pollution, the health impact, indoor air...
CK-12 Foundation
Ck 12: Earth Science: Types of Air Pollution
[Free Registration/Login may be required to access all resource tools.] Distinguishes between primary and secondary pollutants and identifies examples of each.