Photochemical smog is a type of smog that is produced when ultraviolet light from the sun reacts with nitrogen oxides and volatile organic compounds in the atmosphere. It is a brownish-gray haze that is visible with the naked eye. The largest contributor to the formation of photochemical smog is automobiles, while coal-fired power plants and some other power plants also produce the necessary pollutants to facilitate its production. Due to its abundance in areas of warmer temperatures, photochemical smog is most common in the summer. Key features of photochemical smog include:
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Composition: When exposed to ultraviolet radiation, nitrogen oxides go through a complex series of reactions with hydrocarbons to produce the components of photochemical smog, which include a mixture of ozone, nitric acid, aldehydes, peroxyacyl nitrates (PANs), and other secondary pollutants.
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Effects: Photochemical smog has many adverse effects. When combined with hydrocarbons, the chemicals contained within it form molecules that cause eye irritation. Radicals in the air interfere with the nitrogen cycle by preventing the destruction of ground-level ozone. Other effects include reduced visibility, decreased vision, and shortness of breath. Ground-level ozone can prove to be extremely toxic to human beings.
Photochemical smog occurs most prominently in urban areas that have large numbers of automobiles.
