As originally coined in 1905 by Des Voeux: a natural fog contaminated by industrial pollutants, a mixture of smoke and fog. Today, it is the common term applied to problematical, largely urban, air pollution, with or without the natural fog; however, some visible manifestation is almost always implied. Smogs are constituted in great variety, but a major dichotomy exists between the photochemical smogs of nitrogen oxides and hydrocarbons emitted mainly by automobile engines and, on the other hand, the sulfur-laden, sometimes deadly, smogs produced by the large-scale combustion of fuel oil and coal. Both types contain carbon monoxide, carbon dioxide, and a variety of particulates. See Los Angeles (photochemical) smog, London (sulfurous) smog.