Polar Stratospheric Clouds in the Arctic

Abstract

Polar ozone depletion is a major environmental issue, for the alterations induced on the chemical-physical equilibrium of the stratosphere and their impact on planetary climate and ecosystem. Early studies recognized that Polar Stratospheric Clouds (PSCs) play a crucial role in this process, for being the primary surfaces where heterogeneous chemical reactions promote the formation of species responsible for ozone removal. In addition, PSC particle formation scavenges nitric acid and water vapor from the gas phase, causing denitrification and dehydration. As denitrification enhances chlorine radical lifetime, PSCs become a significant element for the chemical balance of the polar stratosphere. A brief survey of the chemistry of the stratospheric ozone and of stratospheric particles is here given, together with an outline of the dynamic of the stratosphere with emphasis on the polar regions. It is then presented the effect of the CFCs in the perturbation of the ozone chemistry in the winter polar stratosphere, and the twofold role of Polar Stratospheric Clouds, promoting the release of active chlorine from its reservoir species and denitrifying the stratosphere upon condensation of nitric acid and further removal by particle gravitational settling, is discussed. A survey of the main scientific activities carried out in the arctic to study the processes in which PSC are involved is then provided. An illustration on PSC formation microphysics theories, and related open issues, ends the chapter.