AIRPACT-2 is an enhanced web-based air-quality forecasting system based on the MM5 meteorological model coupled with a dynamic emissions processing system and the CALMET/CALGRID photochemical grid modeling pair. The system reports hourly concentrations of pollutants in the Pacific Northwest region covering an area from Vancouver, BC in the north to Salem, OR in the south, and from the Pacific coast in the west to beyond the crest of the Cascade Mountain Range in the east.

The objective of this paper is to evaluate the performance of the AIRPACT-2 modeling system against observed concentrations of ozone (O3), particulate matter (PM2.5), and some selected air toxics species, including formaldehyde, acetaldehyde, 1,3-butadiene, benzene and perchloroethylene. for September, 2003. The emphasis in this evaluation is to document the level of performance of the forecast system and to investigate which components of the system contribute most to uncertainties in model predictions.