A molecule that is composed of two oxygen atoms, O2, and has no color, odor, or taste. It is present in both the atmosphere and dissolved in the oceans and freshwater sources exposed to the atmosphere. Solar radiation with wavelengths less then 242 nm can break it back into oxygen atoms, O2 ---> O + O | One of these oxygen radicals in turn can combine with O2 to form ozone, O2 + O ---> O3 | [Science; v265: pages 1817-1818; 1994.] [Science; v235: pages 199-202; 1987.]
