Guidance for the performance evaluation of three-dimensional air quality modeling systems for particulate matter and visibility

Guidance for the performance evaluation of three-dimensional air quality mo deling systems for particulate matter and visibility is presented. Four lev els are considered: operational, diagnostic, mechanistic, and probabilistic evaluations. First, a comprehensive model evaluation should be conducted i n at least two distinct geographical locations and for several meteorologic al episodes. Next, streamlined evaluations can be conducted for other simil ar applications if the comprehensive evaluation is deemed satisfactory. In all cases, the operational evaluation alone is insufficient, and some diagn ostic evaluation must always be carried out. Recommendations are provided f or designing field measurement programs that can provide the data needed fo r such model performance evaluations.