Los Angeles smogsecondary pollution

The air pollutants that we have been discussing so far have come from stationary sources. Traditionally, industrial and domestic activities in large cities burnt coal. The transition to petroleum-derived fuels this century has seen the emergence of an entirely new kind of air pollution. This newer form of pollution is the result of the greater volatility of liquid fuels. The motor vehicle is such an important consumer of liquid fuels that it has become a major source of contemporary air pollution. However, the pollutants really responsible for causing the problems are not themselves emitted by motor vehicles. Rather, they form in the atmosphere. These secondary pollutants are formed from the reactions of primary pollutants, such as NO and unburnt fuel, which come directly from the automobiles. Chemical reactions that produce the secondary pollutants proceed most effectively in sunlight, so the resulting air pollution is called photochemical smog.

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