The construction and use of models aid the understanding of the real thing. Computer models of the atmosphere lead to an understanding of various processes and their interactions. Furthermore, the results of models can identify parameters that are particularly important and suggest laboratory and field experiments that may clarify uncertainties. As computing capabilities improve, more complex models can be constructed. Models generally grow from detailed box models to one- dimensional (altitude dependence), two-dimensional (altitude and latitude), and three-dimensional (altitude, latitude, and longitude) models in which physical and chemical detail is sacrificed for expanded spatial coverage, but the higher dimensional models are designed to capture the essential features of the lower dimensional models. Most models of atmospheric chemistry have been limited to gas phase chemistry. They ignore the role of clouds and aerosol particles. This project will develop numerical models of atmospheric chemistry to include these multimedia systems. The importance of these processes has been highlighted by the discovery of the Antarctic ozone hole which develops, in part, because of the presence of polar stratospheric clouds. The long-range objective is to develop a three-dimensional photochemical model that includes the most useful features of the cloud/aerosol chemical models.
