Regional modeling of particulate matter (PM) using the CMAQ and CAMx photochemical grid models

Particulate Matter (PM) and ozone are important regulatory air quality issues in the United States (US). More recently, the focus has been on fine PM (PM2.5) and 8-hour ozone and visibility whose extent is more regional in nature than the previous focus on urban 1-hour ozone peaks and PM10. The US Environmental Protection Agency (EPA) has formed five regional planning organizations (RPOs) that consist of groups of States and Tribes to address the requirements of the Regional Haze Rule (RHR) and the regional components of the 8-hour ozone and PM2.5 standards. The RPOs are running photochemical grid models to identify the sources that contribute to visibility degradation, PM2.5 and ozone, project future year air quality and visibility and evaluate the effects of alternative emission control strategies. Two primary photochemical grid models are being used for this purpose, the Community Multiscale Air Quality (CMAQ) Modeling System and the Comprehensive Air-quality Model with extensions (CAMx). CMAQ and CAMx represent two state-of-science Ozone/PM models capable of simulating regional ozone using two different platforms. This paper presents the application of CMAQ and CAMx for the 2002 annual period and a comparative model performance evaluation. Three of the RPOs are running the two models side-by-side to address regional PM/ozone/visibility in the western (WRAP), central (CENRAP) and southeastern (VISTAS) portions of the US. Differences in model performance are explained by the differences in model formulation. Areas of improvement in model formulation in both models are identified.