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Name: Kay
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Question:
An atmospheric temperature inversion happens when warm air settles in a layer above cold air. When this condition occurs over cities, it can create a very stable air mass that traps pollution near the Earth's surface. Why is the air mass in a temperature inversion so stable?

Replies:
Kay,

"Stable" is the word used to describe the atmospheric stability when warmer air overlies cooler air (this is called a temperature inversion). The word inversion is used because the air temperature generally decreases with height; but in the case of an inversion, the temperature gradient (change of temperature with height) is inverted, or reversed from normal. This typically

The inversion is meta-stable -- it really is not stable. There are a lot of reasons why/how this can happen. Two common ones are slow moving warm air that "rides up" of colder air because there is not adequate turbulence for the two air masses to mix. The other is a result of mountains forming a 'bowl' trapping the cold air near the ground. Here too the lack of air turbulence is at fault. You can find a detailed description at:

http://daphne.palomar.edu/calenvironment/smog.htm

Vince Calder

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