I run a number of EPA-approved Gaussian air pollution models as part of my research and consulting work. The purpose of these models is to predict the area impact (in terms of concentration and/or surface deposition) due to emissions associated with one or more polluting sources. Examples of such sources are emissions from refineries, chemical plants, fires, pesticide applications on agricultural fields, wind blown dust, as well as many others.
Among the models I run are ISCST3, AERMOD and CALPUFF. Others are listed in my CV.
Part of my air pollution modeling work is done with a team of other consultants at Envirocomp Consulting. The Envirocomp Institute also publishes several e-books on air pollution and environmental modeling techniques.