Technical Abstract: The air pollution regulatory process involves the permitting of sources of regulated pollutants. This process requires sources to demonstrate that the National Ambient Air Quality Standards (NAAQS) are not exceeded as a result of released pollutants. A determination of a facility's compliance with the NAAQS is more frequently being based on dispersion modeling estimates rather than ambient air sampling results. Current Gaussian based dispersion models do not adequately account for pollutant dispersion due to sub-hourly variations in wind speed and direction. This can result in over-estimates of downwind concentration and consequentially require costly additional control measures or denial of a construction or operating permit. This research focuses on developing a methodology to analyze the theoretical degree of dispersion within sub-hourly and hourly intervals. The methodology used to develop the presently used plume spread factors (Pasquill-Gifford [PG] dispersion parameters) is explored and used in developing a new methodology for estimating theoretical plume dispersion parameters based on recorded meteorological data. This comparison allowed for an appropriate application time period of the PG dispersion parameters to be determined, which in general, varied from 3 to 20 minutes. The most critical result of this research is that applying the PG dispersion parameters to a one-hour period is incorrect. This misapplication will result in concentration estimates based on insufficient plume spread, which will over-estimate downwind concentrations and result in inappropriate regulation of emitting sources.