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. Recent advances in dispersion modeling theory have 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. EPA has promulgated the approval of AERMOD dispersion model as the replacement for ISC for evaluating near-field impacts for regulatory purposes. AERMOD requires several additional geophysical meteorological input parameters that ISC does not utilize. To provide guidance as well as to implement the use of AERMOD. the Louisiana Department of Environmental Quality (LDEQ) formed a Modeling Workgroup to evaluate issues with implementing AERMOD and to revise the existing Louisiana Air Quality Modeling Procedures issued in October 1999 to incorporate guidance for using AERMOD .
Workgroup members performed several hypothetical case studies to evaluate AERMOD's behavior in comparison with ISC. The case studies involved source/geography configurations typical to Louisiana industrial facilities. The results of these analyses, along with case studies already put forth by EPA and other groups were used to develop updated modeling guidance. including the development of site-specific parameters required by AERMOD for the various geographic regions of the state.
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. Lastly, the updates to the Louisiana Air Quality Modeling Procedures are discussed.
`Revising Louisiana State Air Quality Modeling Guidance for the Incorporation of AERMOD,` presented at the 2006 A&WMA annual conference