Laboratory Studies of Atmospheric Heterogeneous Chemistry

In the laboratory, ice films formed by freezing from the liquid or more frequently by deposition from the vapor phase have been used to simulate stratospheric cloud surfaces for measurements of reaction and uptake rates. To obtain intrinsic surface reaction probabilities that can be used in atmospheric models, the area of the film surface that actually takes part in the reaction must be known. It is important to know not only the total surface area but also the film morphology in order to determine where and how the surface is situated and, thus, what fraction of it is available for reaction. Information on the structure of these ice films has been obtained by using several experimental methods. In the sections that follow, these methods will be discussed, then the results will be used to construct a working model of the ice films, and finally the model will be applied to an experimental study of HC1 uptake by H_2O ice.