From Glossary of Meteorology
A series of reactions, first proposed by Sidney Chapman in the 1930s, to explain the presence of the ozone layer in the earth's stratosphere.
The reaction sequence is as follows:
where M is any other molecule in the termolecular reaction. Models based only on the Chapman cycle overpredict stratospheric O3 levels, and it is now recognized that additional destruction of O3 occurs through catalytic cycles involving oxides of nitrogen, chlorine, and hydrogen.
Chapman, S. 1930. A theory of upper atmospheric ozone. Mem. Roy. Meteor. Soc.. 3. 103–125.