EVALUATION OF 3 AIR DISPERSION MODELS - ISCST2, ISCLT2, AND SCREEN2 FOR MERCURY EMISSIONS IN AN URBAN AREA

The goal of this paper is to compare and evaluate the performance of t hree air quality regulatory models for mercury releases. The models in clude Industrial Source Complex Short Term model (ISCST2), Industrial Source Complex Long Term model (ISCLT2), and SCREEN2. The evaluation i s conducted in multiple point source urban environment using meteorolo gical data, emission inventory and monitoring data for eight stations for the year 1990 to 1992. The performance of the models is evaluated using eight statistical parameters. The comparison of models results f or both quarterly and annual averaging periods shows that ISCST2 predi ctions qualitatively match the observed concentrations; whereas SCREEN 2 predicts highest concentrations and ISCLT2 the lowest concentrations . The summary of statistical analysis obtained by using three differen t methods of observed concentration (Co) and predicted concentrations (Cp) comparison show that the ISCST2 has a better overall performance than ISCLT2 and SCREEN2 models. However, none of the models met the cr iteria for a reasonable model. Summaries of 95% confidence limits on n ormalize mean square error (NMSE), geometric mean variance (VG) and ge ometric mean bias (MG) for each and among model indicate that of the t hree models, ISCST2 has the best overall performance indicators. Impro ved model performance may be achieved by incorporating different types of mercury forms into emission rate and air dispersion calculations.