Smog is a dense, atmospheric mixture of smoke and fog or chemical fumes, commonly occurring in urban or industrial areas. Smogs generally occur when there is radiation fog. If the air remains calm, the fog gets worse, and more industrial grime accumulates, as it is unable to escape into the atmosphere. The water droplets condense around the pollutants forming thick fog. One of the worst areas for smog is Los Angeles, California. It is a result of the exhaust emissions of the city's vast number of cars. The air pollution is exacerbated by Los Angeles: topography: it lies in a large basin, noted for inversions of temperature, which create ideal conditions for the formation of fogs and smogs.