Abstract

Heterogeneous reactions on polar stratospheric clouds (PSCs) have recently been implicated in Arctic and Antarctic ozone destruction. Although the chemistry is now well documented, there are still major uncertainties in the chemical composition and formation mechanism for PSCs. PSCs are usually classified as type I or type II, depending on their formation temperature. Type II PSCs are composed of crystalline water ice and form only when stratospheric temperatures drop below about 188 K. These clouds are most frequently observed in the Antarctic winter stratosphere. In contrast, Type I PSCs form at temperatures several degrees warmer than the frost point and are therefore observed in both polar stratospheres. Although type I PSCs are thought to contain HNO₃ and water, the exact chemical composition has not been established.

© 1995 Optical Society of America