Polar Stratospheric Clouds and the Ozone Hole

During the winter clouds appear in the Arctic and the Antarctic stratospheres. These clouds have been observed for over a century, and during most of that time they were considered an interesting and beautiful but relatively unimportant phenomenon. Recently, however, atmospheric scientists have found a critical relationship between the massive springtime ozone depletion over Antarctica and the formation of polar stratospheric clouds. (See figure 1.) In this article we outline the general properties of the three main types of stratospheric aerosols, and we show how changes in the levels of stratospheric nitrogen and chlorine species required for ozone depletion are dependent upon the formation of polar stratospheric clouds.