Developing State-Wide Modeling Guidance for the Use of AERMOD – A Workgroup's Experience

摘要

For over two decades, the Industrial Source Complex (ISC) dispersion model has been the primary model used to predict ambient air impacts from stationary sources, particularly in regard to regulatory considerations when permitting new or modified sources. Recent advances in dispersion modeling theory and computational power have led to major improvements over the ISC model. These improvements resulted in the creation of a new type of modeling algorithm referred to as the American Meteorological Society/U.S. Environmental Protection Agency Regulatory Modeling System (AERMOD). The U.S. Environmental Protection Agency (EPA) has proposed replacing ISC with the AERMOD dispersion model for evaluating near-field impacts for regulatory purposes, anticipating adopting it as the standard model by the end of 2005 and phasing out ISC in 2006. This action will have numerous implications for industrial facilities and regulators. AERMOD requires several additional geophysical meteorological input parameters that ISC does not utilize. Much discussion has taken place as to how these parameters should be set, but little overall guidance exists to assist modelers in determining their values. To address this lack of guidance, Louisiana Department of Environmental Quality (LDEQ) formed a Modeling Workgroup to evaluate issues with implementing AERMOD and to develop modeling guidelines for use with AERMOD within the state of Louisiana. Workgroup members performed several hypothetical case studies to (1) evaluate AERMOD’s behavior in comparison with ISC, (2) compare use of on-site meteorological data to National Weather Service (NWS) data, and (3) determine AERMOD’s sensitivity to changes in input land-use parameters. The results of these analyses are being used to develop modeling guidelines, including site-specific parameters required by AERMOD. The paper summarizes the results of analyses performed by Workgroup members, as well as recommendations made by the members. In addition, general differences between ISC and AERMOD are discussed, including processing times, land-use parameters, meteorology inputs, and treatment of terrain.