This paper summarizes the outcome of a study focused on preparing a regional modelling environment that can be used to evaluate the impacts of Canadian and U.S. emissions, from man-made and natural sources, on ozone (O3), fine particulate matter (PM2.5) and visibility within the Pacific Northwest (i.e., northern Oregon, Washington State, and most of southern British Columbia, including the major urban centers of Portland, Seattle, and Vancouver). The study involved: the preparation and conversion of MC2 meteorological data for input into SMOKE and CMAQ, the compilation and processing of emission inventory data, and air quality modelling over nested 12 and 4-km grid resolution domains for two meteorological episodes (summer 2001 and winter 2002). After performing a detailed evaluation of the model performance for the summer 2001 episode using ambient monitoring data collected during the Pacific 2001 field monitoring campaign, numerous trans-boundary and future year emission projection scenarios were modelled. The model evaluation indicates that using high-resolution MC2 model outputs to drive SMOKE and CMAQ resulted in good model performance on both grid definitions. Results from emission scenario runs indicate that urban emissions, including those from marine, mobile and industrial activities, have a significant impact on both local and downwind O3 and PM2.5 levels. Modelling of various trans-boundary and future year emission scenarios indicates that not only regional / synoptic weather patterns, but also localized sea breeze and terrain effects influence the trans-boundary movement of pollutants in this region, although for the episodes modelled, short range transport phenomena occur more frequently than long-range transport.