The Pollution Episodic Model (PEM) is an urban scale (up to 50km distances) air pollution model capable of predicting short-term (1 to 24-hour) average surface concentrations and deposition fluxes of two gaseous or particulate pollutants at up to a maximum of 2500 ground-level receptors located on a 50km by 50km square receptor grid. Predictions are based on steady-state Gaussian plume assumptions, Briggs' plume rise formulations, and Pasquill-Gifford (P-G) dispersion parameters. The surface concentration and deposition flux estimates of two independent non-reactive (gaseous or particulate) pollutants or one pollutant with first-order chemical decay can be obtained as special cases of the model. Up to 300 point sources and up to 50 area sources may be included in the model inputs....Software Description: The model is written in the FORTRAN programming language for implementation on an IBM 3090 computer.