We evaluate the predictive performance of a 12-month, 12km horizontal resolution WRF-Chem air quality model simulation for the contiguous United States. Model performance is comparable to other contemporary models used for regulatory and health-effects analysis, with 12% bias for daytime ozone and -1% bias for fine particulate matter (PM2.5). Performance for PM2.5 is worse in winter and in the western U.S. than in other seasons and regions, suggesting opportunities for future model development.