The AIRPACT-3 air quality forecast system employs daily MM5 meteorological forecasts with dynamic emissions processing and the CMAQ photochemical model to predict gas and aerosol concentrations for a domain encompassing Idaho, Oregon, Washington, and portions of southern Canada. In this work, detailed speciated aerosol data and ozone observations for a four month period from summer and fall, 2004 are used to evaluate the performance of AIRPACT-3.