AERMOD is the U.S. EPA’s recommended model for evaluating near-field impacts, defined as occurring within 50 km of the sources, caused by pollutant emission sources. Since promulgation of the 1-hour NO2 NAAQS in 2010, U.S. EPA has released guidance and made refinements to AERMOD to make dispersion modeling analyses for NAAQS compliance demonstration purposes more “realistic”, that is, more like an ambient concentration that is actually measured at a monitor. In the latest version of AERMOD, released in 2022, U.S. EPA updated the Generic Reaction Set Method (GRSM) option and also designated it as a Beta option, allowing its use for regulatory applications on a case-by-case basis.
This case study reviews 1-hour NO2 concentrations predicted by AERMOD for the Beta GRSM option and for other regulatory default Tier 3 options, the Ozone Limiting Method (OLM) and the Plume Volume Molar Ratio Method (PVMRM), for several hypothetical sources at locations throughout the United States. Also presented are results showing the sensitivity of AERMOD outputs to those inputs needed for the current regulatory and Beta Tier 3 options.
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