Models of cloud chemistry

Clouds and precipitation systems play a very important røle in the transformation and redistribution of chemical species in the atmosphere. Modeling of cloud chemistry is a complicated subject not only because chemistry in clouds is very complex, but also because cloud chemical processes are highly dependent on the microphysics and dynamics of clouds. A general cloud chemistry model must take into consideration the wide range of temporal and spatial scales over which cloud microphysical and dynamical processes take place. In this paper, a review of the basic cloud chemical and microphysical processes are presented. Special emphasis is given to the interactions between chemical and microphysical processes, and to considerations which may lead to model simplifications. SO₂ and NO_x chemistries are used as the main examples, a subject of interest in air pollution and acid rain research. A summary of recent modeling work is also presented.