An air quality model which assumes a form of solution of the equation for a single source, inserts appropriate empirical parameters, and sums the solutions over all sources is described. Three categories of source are recognized in the model: major, intense, discontinuous, i.e., point and line, sources (examples are the stacks of electrical generating or other major industrial plants and highways, etc.); numerous minor sources which are treated as continuous area sources; and sources beyond the boundary of the model. Special devices, effectively a sub-model, which were needed to deal with the proximity of very large sources, unknown in detail, in the area of New York City are described. (Author)