In normal weather situations, the surface air is warmed by the heat radiating from the earth's surface and the sun's rays. It then rises upward, into the atmosphere, to be cooled through a convection-type heat that expands with the cooler upper air. As the warm air rises, the surface pollutants are carried upward and dissipated into the atmosphere.
When a temperature inversion occurs, we find the higher air is no longer cooler but, rather, is warmer than the surface air, causing the cooler surface air to become trapped and unable to move. This warm air blanket can extend from above ground level to a few hundred or even a few thousand feet high. As the surface air is trapped, so are the pollutants, causing a severe smog condition. Should this stagnant air mass extend to a few thousand feet high, enough air movement with the inversion takes place to allow the smog layer to rise above ground level, but the pollutants still cannot dissipate. This inversion can remain for days over an area, with only the smog level rising or lowering from ground level to a few hundred feet high. Meanwhile, the pollutant levels increase, causing eye irritation, respiratory problems, reduced visibility, plant damage and in some cases, cancer-like diseases.
This inversion phenomenon was first noted in the Los Angeles, California area. The city lies in a basin-type of terrain and during certain weather conditions, a cold air mass is held in the basin while a warmer air mass covers it like a lid.
Because this type of condition was first documented as prevalent in the Los Angeles area, this type of smog was named Los Angeles Smog, although it occurs in other areas where a large concentration of automobiles can be found and the air remains stagnant for any length of time.