Vertical temperature structure

As you will learn in much greater detail in later readings, the temperature in the atmosphere changes (generally decreasing) as one goes higher. The rate at which the temperature changes is known as the atmospheric lapse rate. The lapse rate is an indicator of the stability of the atmosphere, which has a direct influence on the formation, transport, and dispersion of air pollutants. More specifically, the stability of the atmosphere affects the vertical mixing that can occur. Strong stability in the atmosphere (a temperature increase with height), limits mixing, which reduces the amount of dilution that can occur.
(Click on image to see full-sized)

The graphic above right (click on image to see larger) shows the changes in temperature as a function of height. Notice particulary that the lapse rate is negative (getting colder) in the troposphere, until the tropopause is reached.

A temperature inversion (increase in temperature with height) is the way we recognize strong stability. Temperature inversions trap emissions (primary pollutants) and products such as ozone (a secondary pollutant) nearer to the ground. For example, the two graphics below show the normal decrease in temperature with increasing height (shown on the left) and an inversion (shown on the right), in which there is a temporary increase in temperature before it returns to a decreasing slope:

Graphic of normal temperature decrease with heightGraphic of a temperature inversion

You might also notice in these diagrams, that the temperature begins to increase around 10 km. As in the larger graphic at the top of the page, this signifies the beginning of the tropopause.

Quick Quiz: Typically, the beginning of the tropopause is indicated by what?
The tropopause is always at a height of about 15 km
A decrease in temperature with height
An increase in temperature with height
The tropopause cannot be determined by height or by temperature

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