A few common air pollutants are found all over the United States. These pollutants can injure health, harm the environment and cause property damage. Although EPA has been regulating criteria air pollutants since the 1970 CAA was passed, many urban areas are classified as nonattainment for at least one criteria air pollutant. It has been estimated that about 90 million Americans live in nonattainment areas. Smog What we typically call smog is primarily made up of ground-level ozone .
Ozone can be good or bad depending on where it is located.
Ozone in the stratosphere high above the Earth protects human health and the environment, but ground-level ozone is the main harmful ingredient in smog. Ground-level ozone is produced by the combination of pollutants from many sources, including smokestacks, cars, paints and solvents. When a car burns gasoline, releasing exhaust fumes, or a painter paints a house, smog-forming pollutants rise into the sky. Often, wind blows smog-forming pollutants away from their sources. The smog-forming reactions take place while the pollutants are being blown through the air by the wind.