Definition of "smog" [smog]

• Fog that has become mixed and polluted with smoke. (noun)
• A form of air pollution produced by the photochemical reaction of sunlight with hydrocarbons and nitrogen oxides that have been released into the atmosphere, especially by automotive emissions. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "In general the term smog has become connected to a situation where visibility is significantly impaired as a result of local air pollution."
• "The term smog, a contraction of smoke and fog, was introduced in 1905 by Dr. H.A. des Vœux to describe the mixture of soot, sulfuric acid, and other pollutants in emissions from coal furnaces in London."
• "The term smog was first used in 1905 to describe the conditions of fog that had soot or smoke in it."