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Photochemical Smog

  • By: Julie Wallace
  • In: Encyclopedia of Geography
  • Edited by: Barney Warf
  • Subject:General Geography, Earth & Environmental Science

Photochemical smog is a noxious mixture of pollutants formed in the presence of sunlight. It is very harmful to humans, animals, and plants. The ingredients required for the production of photochemical smog are oxides of nitrogen (NOx), volatile organic compounds (VOCs), and sunlight. NOx and VOCs are themselves harmful, but in the presence of sunlight, they are involved in a complex series of reactions that create other harmful substances. Industry and transportation sources contribute most of the precursor gases. Photochemical smog is, therefore, most prevalent in urban areas. Ground-level ozone (O3), a secondary pollutant created by reactions between the precursor gases, is the main component of photochemical smog.

Nitric oxide (NO) is emitted when hydrocarbons such as gasoline, diesel fuels, or coal are burned. It is ...

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