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Clean Air
Clean air is a mixture of about 78 percent nitrogen; 21 percent oxygen; less than 1 percent of carbon dioxide, argon, and other gases; and varying amounts of water vapor.

What is air pollution?
If there are other particles or gases in the air that are not part of its normal composition, we call this "air pollution" and the particles or gases are called "air pollutants." Very small amounts of certain air pollutants can cause serious health and environmental problems.

We can see some air pollutants such as the reddish-brown haze in smog; however, other air pollutants, including some of the most dangerous, are invisible.

Air pollution can be natural or human-made. Air pollution occurs naturally during volcano eruptions, forest fires, or dust storms. This has been an occasional problem for humans. However, during the past hundred years, air pollution created by humans has become a major, persistant problem. In California, our cities are among the smoggiest urban areas in the country.

For more suggestions, check out Whatcha Doin' About Air Pollution
and 50 Things You Can Do for Cleaner Air.