An air-quality forecasting (AQF) system based on the National Weather Service (NWS) National Centers for Environmental Prediction’s (NCEP’s) Eta model and the U.S. EPA’s Community Multiscale Air Quality (CMAQ) Modeling System is used to simulate the distributions of tropospheric ozone and particulate matter (PM) over the eastern United States during the summer of 2004. The refinements and adaptation of the CMAQ model for PM forecast applications will be discussed. The ability of the model to forecast the co-evolution of surface level ozone and PM pollution will be assessed through comparisons with regional ozone and continuous PM2.5 measurements from the AIRNOW system. Analyses of the strengths and weaknesses of the modeling system in representing the fine PM chemical constituents through comparisons with speciated measurements from the IMPROVE, CASTNet, and STN networks will be discussed. Preliminary comparisons of model forecasts with available aircraft measurements from the 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field study will be presented.

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