There are many different chemical substances that contribute to air pollution.  These chemicals come from a variety of sources.

Among the many types of air pollutants are nitrogen oxides, carbon monoxides, and organic compounds that can evaporate and enter the atmosphere.

Air pollutants have sources that are both natural and human.  Now, humans contribute substantially more to the air pollution problem.

Forest fires, volcanic eruptions, wind erosion, pollen dispersal, evaporation of organic compounds, and natural radioactivity are all among the natural causes of air pollution.

Usually, natural air pollution does not occur in abundance in particular locations.  The pollution is spread around throughout the world, and as a result, poses little threat to the health of people and ecosystems.

Though some pollution comes from these natural sources, most pollution is the result of human activity.  The biggest causes are the operation of fossil fuel-burning power plants and automobiles that combust fuel.  Combined, these two sources are responsible for about 90% of all air pollution in the United States.

Some cities suffer severely because of heavy industrial use of chemicals that cause air pollution.  Places like Mexico City and Sao Paulo have some of the most deadly pollution levels in the world.

Toxic substances from Motor Vehicles