Reduces ozone in stratosphere. Has been phased out of gasoline, which has considerably reduced the contamination of air by lead. In upper atmosphere, ozone shields the Earth from ultraviolet rays. At ground level it is a pollutant with toxic effects. Can also damage trees and plants and reduce visibility.
Nitrogen oxides react with volatile organic compounds to form smog.
Produced from burning fuels, including gasoline and coal. Aside from reducing visibility and soiling clothing, microscopic particles in the air can be breathed into lung tissue becoming lodged and causing increased respiratory disease and lung damage. Particulates are also the main source of haze, which reduces visibility. Produced by burning coal, most notably in power plants. Major contributor to smog and acid rain.