Formation mechanisms of polar stratospheric clouds

The physical chemistry of polar stratospheric clouds is far from being well-understood and the uncertainties affect our understanding of polar ozone destruction, in particular in the northern stratosphere. However, the scientific field is very rapidly developing. This paper summarizes the current state of our knowledge of the microphysics and heterogeneous chemistry of polar stratospheric clouds with emphasis on liquid and solid particle thermodynamics and on kinetics of non-reactive gas uptake leading to particle growth. The consequences of the present uncertainties for the chemical processing of stratospheric air are briefly discussed.