Sensitivity of AERMOD concentration predictions to variations in several input parameters

The AERMOD air quality model is an advanced plume model that is being proposed for regulatory use. This model is the result of an effort to incorporate scientific knowledge gained over the last three decades into regulatory plume models. Studies previously reported indicate significant improvements in the ability to of AERMOD, over the traditional Gaussian models, to predict measured concentrations. It is also important to know the sensitivity of model results to changes in various input parameters. This information is needed to gauge the accuracy required for these input parameters. Such information can also help determine whether a model is excessively sensitive to variations in certain input parameters. Of particular interest for regulatory applications are the effects of changes in input parameters on design concentrations such as the highest or high-second high 1-hour, 3-hour, and 24-hour concentrations, and the annual average concentrations.

This study identifies the sensitivity of these design concentrations predicted by AERMOD to changes in several input parameters, including albedo, surface roughness length, Bowen ratio, latitude of the site, pollutant release height, and plume rise. A base case model run is prepared for each of two sources, a near-surface source and an elevated buoyant source. Meteorology for a site in the central use is used. Each of these input parameters is perturbed upward and downward by amounts ranging from 10% to the highest and lowest values expected in most modeling applications. The results are analyzed, and conclusions drawn regarding the implications of these results on modeling applications. Specific attention is given to accuracy requirements for these parameters and any indication that the model may be excessively sensitive or insensitive to any of the parameters.