Smog may refer to:
Smog is a type of air pollutant. The word "smog" was made in the early 20th century as a portmanteau of the words smoke and fog. The word was then intended to refer to what was sometimes known as pea soup fog, a problem in London from the 19th century to the mid 20th century, caused by the burning of coal within a city; this smog contains soot particulates, sulfur dioxide and other components. Modern smog, as found for example in Los Angeles, is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form photochemical smog. It is toxic to humans and can cause sickness, shortened life or death.