Evaluation of AERMOD model performance under building downwash conditions

The AMS/EPA Regulatory Model Improvement Committee (AERMIC) has recently completed development of the AERMIC Model (AERMOD). AERMOD has been developed as a possible replacement for the EPA's Industrial Source Complex (ISC3) dispersion model for regulatory modeling of point, volume and area sources. AERMOD includes improved algorithms for plume rise, plume dispersion, treatment of the vertical inhomogeneity of the planetary boundary layer, treatment of plume interactions with the elevated inversion layer, and influences of elevated terrain. The AERMOD model has also been evaluated on a total of ten databases. One area of algorithmic improvement that has not yet been accomplished for AERMOD is for building downwash influences. AERMOD includes the same downwash algorithms as are in the current regulatory version of ISC3. The Electric Power Research Institute (EPRI) has recently completed development and evaluation of new downwash algorithms, which have been incorporated into a version of the ISC3 model called ISC-PRIME. This paper presents results of an evaluation of the current version of AERMOD on the Bowline Point Station database used in the independent evaluation of ISC-PRIME. The Bowline data consists of a full year of on-site meteorological data with monitored SO2 data at four receptor locations for an electric generating facility located in the Hudson River valley in New York. The evaluation results include a statistical evaluation of model performance following EPA-recommended procedures, as well as Quantile-Quantile (Q-Q) plots of observed versus predicted concentrations, and other diagnostic results. The results of AERMOD are also compared to the results for ISC3 and ISC-PRIME.