Enhancement and evaluation of the AIRPACT ozone and PM_2.5 forecast system for the Pacific Northwest

Abstract

The Air Indicator Report for Public Access and Community Tracking (AIRPACT) real‐time numerical air quality forecast system operates daily in the Pacific Northwest region to predict hourly ozone, PM 2.5 and related precursor and pollutant species. In an update to the existing AIRPACT forecast system, the MM5/SMOKE/CMAQ Eulerian modeling system replaces the MM5/CALMET/CALGRID model framework. The new system, AIRPACT‐3, has a larger domain that encompasses Washington, Oregon, Idaho, and bordering areas. The system includes a highly dynamic emission processing subsystem which incorporates anthropogenic and biogenic emissions, as well as real‐time wildfire emission estimates, and a dynamic dairy ammonia emissions module. As an initial evaluation of the system, forecast results were compared against measurement data for the August–November 2004 period. Analyses showed that the system is skillful in predicting episodic ozone conditions (8‐h daily maxima) above 50 ppbv, but systematically over‐predicts levels less than 40 ppbv. For fine particulate matter, PM 2.5 , the system captures the concentration differences between urban and rural regions, and captures qualitatively the speciated distribution of fine PM 2.5 component concentrations. A separate emission sensitivity study shows the system can adequately simulate the PM pollution impacts from fire events; however, the new dairy ammonia emission module has lesser impact on the overall PM 2.5 forecast performance.