The problems of smog formation are exacerbated by a meteorological phenomenon known as thermal inversion. Under normal atmospheric conditions, warm air in the vicinity of a large city is trapped by an overlayer of cool air. Since warm gases tend to rise, they normally diffuse upward and disperse the smog and other pollutants. A thermal inversion occurs when the upper layer is a layer of warm air, while the polluted air near the ground is relatively cool. In such a situation, the pollutant-laden cool air cannot rise and disperse. Thermal inversion is stabilized by specific geographical features, especially near-by mountains. The local geography of cities like Los.
