Comparison of AERMOD, ISCST3 and ISCST3-Prime: Implications for Risk Assessment.* K. C. Silverman, J. G. Tell, J. Z. Diver, and Z. Qiu, Merck & Co., Inc., New Jersey Institute of Technology
Air quality models are typically used to predict the fate and effects of air emissions from industrial sources to comply with federal and state regulatory requirements and environmental standards, as well as determine pollution control requirements. The current U.S. Environmental Protection Agency (EPA) Industrial Source Complex (ISC) model is a widely used steady-state Gaussian plume model that has the ability to model several source types. In April 2001, the EPA issued a proposed new rule adding several new air quality models to the Guideline on Air Quality Models. The EPA’s Guideline provides technical guidance on the application of air dispersion models for assessing air pollutants under the Clean Air Act (CAA). In the Guideline the EPA proposed replacing the current version of ISC (ISCST3) with AERMOD, a state-of-the-practice air dispersion model, in many air quality impact assessments that now use ISCST3. The Guideline also proposes using ISC-PRIME, a version of ISCST3 that incorporates a new and significantly improved building downwash algorithm. This study evaluated the implications of these proposed model changes as they relate to the assessment of human health risk under the CAA. The air emissions data from the air quality models is the first step in the risk assessment process. The models were tested on point and non-point sources, located on two facilities with differing terrain, and using real meteorological data. The modeled short term and annual ground level air concentrations were used to calculate potential health risks for human receptors. Controlling differences between the air dispersion models and their subsequent impact on the determination of residual risk are identified.
*Best Paper Finalist.
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