Thermal inversion occurs when a layer of warm air settles over a layer of cooler air that lies near the ground. The warm air holds down the cool air and prevents pollutants from rising and scattering. Click here for animated diagram.

A condition that occurs when a layer of warm air forms above a cooler layer of air, trapping pollution in the cooler layer.

A phenomenon in which a layer of cold air above a layer of warm air close to the ground prohibits the dispersion of atmospheric pollution, such as vehicle exhausts.