Warm air has formed a layer on top of cooler surface air. This layer is called the temperature inversion. This means that temperatures actually rise as we measure farther up into the air. Little or no mixing occurs and concentrations of atmospheric particulate pollution and vapors are trapped below the level where temperatures again decrease with altitude. This point is referred to as the top of the inversion.
Inversions can occur at the surface or aloft in the atmosphere.
Those close to the surface have the greatest influence on air quality because air pollution has little room to be dispersed. In this graph, the temperature initially is increasing with altitude. At about the 300 meter mark, the top of the inversion, the temperature pattern is beginning to revert to normal. This inversion means that instead of having virtually endless amounts of air in which to dissipate, our daily air pollution might be confined to a space only 1500 feet above the ground's surface. For more information about temperature inversions, check out weather web sites hosted many universities and the National Weather Service .