The purpose of this study is the evaluation of two Gaussian point source dispersion models by use of hourly meteorological, air quality and emissions data collected at 4 power plant monitoring networks. Two versions of the EPA CRSTER model, CRSTER (Turner) and CRSTER (Irwin), were evaluated. CRSTER (Turner) is the current EPA CRSTER Model which used the so called Pasquill-Gifford-Turner (P-G-T) dispersion curves. CRSTER (Irwin) is a modification of the model based upon Irwin's horizontal and vertical dispersion curves. These models differ only in the choice of horizontal and vertical plume dispersion coefficients (sigma (y) and sigma (z)) and wind profile coefficients. The data for this model evaluation consists of hourly emissions, meteorological and SO2 concentration data collected during the period 1974-1977 at the following networks operated by American Electric Power (AEP): Clifty Creek, Tanners Creek, Muskingum and Gavin-Kyger-Sporn. Three general approaches were used in this analysis: statistical summaries (Chapter V), a comparison of the characteristics of the observed and calculated 3-hour and 24-hour episodes (Chapter VI), and an analysis of selected individual episodes (Chapter VII).