Impact of Local Pollution and Biomass Burning on Air Quality in the Pacific Norwest During the PNW2001 August Intensive

From 1974 to 2000, Enumclaw, WA, has exceeded the 8-hour, 80 ppbv O₃ limit 31 times. As the National Ambient Air Quality O₃ Standard moves to this lower level and the population in the Pacific Northwest continues to increase, understanding and forecasting potentially harmful air quality days will become more important. Three research flights were conducted as part of the PNW2001 field study in the Puget Sound region to examine the spatial distribution of O₃ and aerosol loadings during August 2001. Comparisons to and validations of forecast mode CALGRID O₃ model results were also made. A local pollution episode was measured on August 10 with elevated O₃ (~80 ppbv) and aerosol scattering coefficients (~35 Mm^-}{1) measured downwind of Seattle and Tacoma. These findings are consistent with previous studies but differ in the location of the pollution plumes compared to the forecast mode CALGRID model results. Biomass burning emissions were also encountered in a broad layer above a well-defined temperature inversion on August 16. Meteorological analysis and satellite imagery suggest the elevated O₃ (~60 ppbv) and very high aerosol scattering coefficients (~80 mM^-}{1) were due to emissions from fires burning in Washington, Oregon, and Northern California. These results provide evidence of enhanced O₃ and aerosol scattering, extending to 4 km over Puget Sound, from varying sources. They further demonstrate the capabilities of the CALGRID O₃ forecast model and the need to include biomass burning emissions in this model.