Chemical Composition

The chemical composition of the earth's atmosphere is best characterized in two regions, the homosphere corresponding to the combined troposphere, stratosphere, and mesosphere, and the heterosphere which includes the outer regions of the atmosphere including the exosphere and the thermosphere. This figure summarizes the chemical species and chemical changes that dominant in each of these regions.

Quick Quiz: Which of the following statements about the ionosphere is true ?

The ionosphere is a subunit of the troposphere.
The ionosphere is one region of the atmosphere where the photoionization does not occur.
The ionosphere is the region of the atmosphere where free radical chemistry is most prevalent (compared to other regions).
The ionosphere is part of the homosphere.

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