Photochemical Smog

( Article Type: Explanation )

Photochemical smog comprises a number of chemicals, mainly ozone, aldehydes, peroxyacetylnitrates (PANs) and nitric acid. These substances are formed through the action of strong sunlight upon a mixture of hydrocarbons and nitrogen oxides released into the air from vehicles and industrial processes. The severity of the smog is linked to the atmospheric concentrations of ozone at ground level. In the past, the city of Los Angeles in the USA has experienced serious problems with photochemical smog. To combat this, the city introduced programmes to restrict the number of vehicles travelling on freeways when climatic conditions develop that encourage the formation of photochemical smog. South Africa has not generally seen the development of severe photochemical smog though it does, in certain areas such as Cape Town, experience the effects of smog caused by a combination of inversions and excessive pollution during the winter.