The Community Multiscale Air Quality (CMAQ) modeling system is examined for its ability to predict particulate material (PM) concentrations in the Pacific Northwest. Particulate matter pollution in the Pacific Northwest is unique due to few large pollution point sources and to the large contribution of biomass burning. The worst particulate pollution occurs on cold, stable, stagnant days when wood stoves are heavily used. Strong inversions trap PM close to the surface and often concentrate it in narrow valleys around the Puget Sound. Summertime PM is photochemically produced during mesoscale stagnation events. These episodes impact visibility in the numerous Class I areas in the region. Transport is important from other urban areas such as Portland, OR and Vancouver, BC as well as from forest fires east of the Cascade mountain crest.

To understand PM and gaseous pollution in this region, Pacific Northwest National Laboratories and others conducted the Pacific Northwest 2001 (PNW2001) campaign in August, 2001. This was done in concert with Pacific 2001, a Canadian study of pollution in the Lower Fraser Valley of British Columbia and northwest Washington. PNW2001 provides extensive airborne and ground-based measurements of air pollutants, gaseous precursors, and meteorological variables. It is the most comprehensive and current air quality campaign for this region. CMAQ simulations were performed using 4 km gridded domains for August 20th, 26th, and 27th, the days when the most intensive observations were conducted. The states of Washington, Oregon, and Idaho as well as Environment Canada provided a ground-up emissions database for this study. MM5 produced meteorological fields using a combination of analysis nudging at the coarse resolution and observation nudging to winds at the fine scale. The CMAQ modeling results are compared to aircraft and ground measurements. Preliminary results have shown a large under-prediction of aerosol number concentration. A more thorough analysis of model performance will be presented.