Smoke
Fog
Smoggy foggy afternoon in west Los Angeles, California. Smog

Smog

Smog is a symptom of air pollution, and is used to describe smokey fog. Originally "smog" was used to describe the pea soup fog that sometimes enveloped London in the 19th century. The coinage of this word is credited to Dr. Henry Antoine Des Voeux in his 1905 paper, "Fog and Smoke" for a meeting of the Public Health Congress. Smog occurs when emissions from industry, motor vehicles, incinerators, open burning and other sources accumulate under certain climatic conditions.

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Photo gallery of the great smog of London: In 1952 a thick yellow smog brought London to a standstill for 4 days and is estimated to have killed more than 4,000 people.