Trinity Consultants

Comparison of Two Dispersion Models: A Bulk Petroleum Storage Terminal Case Study

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Courtesy of Trinity Consultants

In 65 FR 21506 (dated April 21, 2000), the United States Environmental Protection Agency (U.S. EPA) proposed revisions to its air dispersion modeling guidance, found in 40 CFR 51, Appendix W (“Guideline on Air Quality Models”) that included replacing the Industrial Source Complex (ISC) model with the American Meteorological Society (AMS) / EPA Regulatory Model (AERMOD) as the regulatory default model for state and federal permitting applications. It is expected that when this switch is finally promulgated, there will be an interim period during which results from either ISC or AERMOD will be considered acceptable. For this reason, it is both interesting and useful to explore differences in pollutant concentrations predicted by each model in a variety of industrial contexts. This study presents a comparison of the pollutant concentration predictions from the AERMOD and ISC (ISCST3 and ISC-PRIME) air dispersion models in the context of fugitive storage tank emissions at a bulk petroleum storage terminal. Data are presented that shows that ISC consistently predicts higher overall and higher maximum pollutant concentrations when compared with AERMOD in this particular situation. This trend is most pronounced when using a volume source to simulate fugitive tank emissions and least pronounced when using an area source. Predicated concentrations can vary for different facility configurations, in regions of differing terrain, and for different meteorological data sets. For this reason, this study should be viewed as an example of one application of these two dispersion models and not as a general treatment of predictions resulting from these models in all applications.

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