Statistical evaluation of centreline concentration estimates by atmospheric dispersion models

Within the American Society for Testing and Materials (ASTM) a standard practice (26849Z(1)) is being developed to provide an objective statistical procedure for comparing air quality simulation modelling results with tracer field data. The practice is limited to steady state, local-scale transport from isolated point sources in simple terrain. Evaluation data having similar external conditions are grouped together, and comparisons are made of the model's ability to replicate without bias the average of the centreline maximum concentrations for each group. Centreline concentrations measured during three field studies are compared with estimates from three steady-state plume models: Industrial Source Complex (ISC), Hybrid Plume Dispersion Model (HPDM) and AMS/EPA Regulatory Model (AERMOD). These results combined with those presented in Irwin and Rosu (1998) provide a complete examination of the draft ASTM standard practice under development. It is concluded that the evaluation methodology is capable of objectively discerning differences in skill between models in their ability to estimate the centreline maximum concentration.