1. Fog that has become mixed and polluted with smoke.
2. 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.

[SM(OKE) + (F)OG¹.]

WORD HISTORY   New phenomena require new words, so it is not surprising that smog is a relatively recent coinage. The word followed the phenomenon by perhaps half a century, for air pollution was first noticed during the Industrial Revolution. The word smog is first recorded in 1905 in a newspaper report of a meeting of the Public Health Congress. Dr. H.A. des Vœux gave a paper entitled "Fog and Smoke," in which, in the words of the Daily Graphic of July 26, "he said it required no science to see that there was something produced in great cities which was not found in the country, and that was smoky fog, or what was known as 'smog.'" The next day the Globe remarked that "Dr. des Vœux did a public service in coining a new word for the London fog."

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.