An evaluation of the AMS/EPA Regulatory Model (AERMOD) complex terrain algorithms

A draft version of the AMS/EPA Regulatory Model (AERMOD) was made available to the public at the Sixth Conference on Air Quality Modeling, in August 1995. The model was also made available to beta testers as part of AMS and EPA`s on-going efforts to thoroughly evaluate the model prior to delivering a completed model to EPA for regulatory use. Since that time, AERMOD has undergone extensive diagnostic evaluation and some changes, with the goal of finalizing the model and subjecting it to performance evaluations with independent data bases prior to releasing the model for general use. The present study documented in this paper was initiated in the beta-testing program and has been continued under the sponsorship of the Maryland Department of Natural Resources Power Plant Research Program (PPRP). The study consists of an in-depth comparison of the complex terrain component of AERMOD, with a focus on neutral and stable-case impacts. Hourly concentration comparisons are made for a wide spectrum of synthesized meteorological conditions and for a broad range of stack characteristics representative of Maryland power plant stacks, between AERMOD predictions and predictions made by other available complex terrain models. The other models included the screening models RTDM and COMPLEX-I, andmore » EPA`s refined CTDM. Predictions are also made and comparisons compiled based on alternative model options within AERMOD. The paper addresses model component-specific impacts in the case of CTDM and AERMOD, i.e. the LIFT and WRAP components representing flow above and around terrain, respectively, and uses graphical representation of model predictions extensively to illustrate model predictions. The paper describes the study approach, provides tabular and graphical summaries of the model and component-specific results, and offers some interpretations of model performance based on these intercomparisons.« less