Effects of meteorological and emissions conditions on the performance of NOAA Air Quality Forecasting Systems with two different chemical mechanisms

NOAA national Air Quality Forecasting System (AQFS) is composed of North American Mesoscale (NAM) meteorological model and the Community Multiscale Air Quality (CMAQ) atmospheric chemistry transport model. Daily ozone forecasting simulations for the conterminous US (CONUS) domain are made utilizing the operational and experimental configurations with two versions of Carbon Bond (CB) chemical mechanisms, CB-IV and CB05, respectively. Previous studies revealed small wintertime differences between the two mechanisms but relatively large differences in summer. It was also reported that the largest differences often occurred at areas with higher ozone concentrations causing occasional instances of false alarm by the CB05 mechanism in certain urban areas while improving hit rate for peak ozone. Regions with large biogenic emissions also showed large discrepancy between the two mechanisms. The continuous simulation results of AQFS with the operational and experimental configurations provide an opportunity to investigate how the mechanism differences are affected by meteorology and by anthropogenic and biogenic emissions during the entire ozone season. Some preliminary evaluation of the air quality forecasting results showed sensitivity to the synoptic weather conditions affecting atmospheric humidity, temperature and geographical features such as areas with coastal outflows and high altitudes. In this presentation the forecasting results are classified with the weather patterns and emission conditions to characterize the behavior of the model biases caused by the differences in the chemical mechanism formulation.