Short-term air quality forecasts for the Pacific Northwest and long-range global change predictions for the United States

This dissertation presents the development and evaluation of a comprehensive numerical air quality modeling system designed to provide daily forecasts in the Pacific Northwest. The system was also applied to predict the impact of global change upon air quality in the future for the US. This system employs the EPA Community Multi-scale Air Quality (CMAQ) model to treat photochemical gas and aerosol formation, transport and deposition.; For short-term regional air quality forecasts, CMAQ was coupled with the University of Washington meteorological forecast operations using the MM5 weather model to create a regional system called AIRPACT-3. An important aspect of the development was the use of an automated, dynamic emissions processing system. The detailed evaluation of the system against observational data covering a four month period showed the system performed well. For ozone, it correctly predicted high episodic conditions, but over-predicted lower observed concentrations. For PM2.5, it captured concentration variations between urban and rural regions, and concentrations of nitrate and ammonium PM2.5 components, but under-predicted sulfate PM2.5.; For global change impacts on US regional air quality, the CMAQ model was employed along with MM5 to downscale results from the Parallel Climate Model and the MOZART2 global chemistry model based upon the IPCC A2 'business as usual' scenario. US anthropogenic emissions were projected using the EPA EGAS economic model and biogenic emissions were projected using the MEGAN model with adjusted land use. Evaluation using a decade of ozone measurements showed that the system reproduced episodic conditions (defined as the 98 th percentile of daily maximum 8-hr concentration) with a predicted average US concentration of 93 ppbv and a measured concentration of 90 ppbv. Predictions for 2045-2054 indicated poorer air quality for the selected future scenario. The results showed that the future average daily maximum 8-hour ozone concentration will increase 8 ppbv, and larger areas of the US will be impacted at ozone levels greater than 80 ppbv. Additional simulations showed changing future land use and land cover scenarios significantly reduced the magnitude and spatial distributions of future biogenic emissions, which subsequently reduced ozone and secondary organic aerosol levels in the future.