This performance evaluation compares a full annual simulation (2001) of Community Multi-scale Air Quality (CMAQ) (Version 4.4) covering the contiguous United States against monitoring data from four nationwide networks. This effort, which represents one of the most spatially and temporally comprehensive performance evaluations of the model, reveals that CMAQ varies considerably in its ability to simulate ambient air concentrations of critical gas and particulate matter species. Simulations of the peak 1- and 8-h ozone (03) concentrations during the "O-3 season" (April-September, 2001) were relatively good (correlation (r) = 0.68, 0.69; normalized mean bias (NMB) = 4.0%, 8.1%; and normalized mean error (NME) = 18.3%, 19.6%, respectively). The annual simulation of sulfate (SO42-) was also good (0.77 <= r <= 0.92, depending upon network) with relatively small error (25.0%<= NME <= 42.0%), though slightly negatively biased (-2.0%<= NMB <=-10.0%).The quality of ammonium (NH4+) simulations is similar to that pf SO42- (0.56 <= r <= 0.79; -4.0%<= NMB <= 14.0%, 35.0% <= NME <= 63.0%). Simulations of nitrate (NOD, elemental carbon (EC) and organic carbon (OC) are relatively poor, as compared to the simulations of the other species. For NO3-, the simulation resulted in: 0.37 <= r <= 0.62; -16.0%<= NMB <= 4.0%; 80.0%<= NME <= 94.0%. For the carbon species, the r ranged from 0.35 (OC) to 0.47 (EC), with fairly large amounts of error (NME = 68.0% for OC, 58.0% for EC) though small amounts of bias (NMB = -6.0% for EC and 12% for OC). The quality of the PM2.5 Simulations, like PM2.5 itself, represented a compilation of the quality of all of the simulated particulate species (0.51 <= r <= 0.70, NMB = -3.0% and 45.0%<= NME <= 46.0%). Published by Elsevier Ltd.
