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What are the components of smog?

Photochemical air pollution, or photochemical smog, is the result of a number of complex chemical reactions. Nitrogen oxides and hydrocarbons, pollutants released in car exhaust fumes, are the raw materials for photochemical (based on the chemical action of light) reactions. In the presence of oxygen, these pollutants react with strong sunlight to produce a surface layer of ozone.

Whereas it's difficult to see photochemical smog at ground level, when looking down from above it appears as a whitish or brownish haze. Photochemical smog is irritating to the eyes and throat and is a growing summertime problem in urban areas.

Photochemical smog is different from the pea-soup-type smog of London, which is a combination of sulfurous smoke and fog.

Sources: Engelbert, Phillis. The Complete Weather Resource, vol. 3, p. 509; Miller, E. Willard, and Ruby M. Miller....

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