If a minor source fails the screening analysis during review of the application, the permit process may be delayed if a refined analysis is required. Consequently, applicants for minor source permits should consider the pros and cons of submitting a modeling analysis along with the permit application to prevent unnecessary delays. Ambient air monitors can only provide information as to current air quality. They do not predict impacts from new or modified sources. Therefore, ambient impacts from sources that do not yet exist must be determined with predictive tools such as air quality models.
Models allow one to estimate air quality in the future and to explore potential control strategies.
For existing sources, models provide a relatively inexpensive alternative to conventional monitoring studies where field equipment measures the actual concentration of a pollutant in ambient air. That is, models provide a cost effective way to analyze impacts over a wide spatial area where factors such as meteorology, topography, and emissions from nearby sources could be important. Models are not subject to the temporal limitations of most monitoring studies. A wide variety of meteorological conditions can be examined with models.