Middle-latitude cyclogenesis and evolution is one of the key factors in understanding elevated pollution episodes in the United States. Distributions of synoptic patterns and the movement of frontal systems have significant impacts on regional air quality through both production and removal mechanisms of air pollutants. While high photolysis rates and widespread subsidence associated with high-pressure systems favors chemical production and accumulation of air pollutants, dynamic dilution and wet deposition associated with frontal systems are very efficient pathways for the removal of many pollutants. Simulation results from the Community Multiscale Air Quality (CMAQ) model over the conterminous U. S. domain and surface observations have been analyzed to investigate the behavior of air pollutants and the model's performance associated with frontal activity. Using geographic information system (GIS) technology, 3-hour weather bulletins from National Centers for Environmental Prediction (NCEP) of the National Weather Service (NWS) have been used to track individually the evolution and movements of middle-latitude synoptic systems. Analysis shows that the occurrence of a particular air pollution episode is strongly related to the evolutionary change in the locations of emission sources relative to a frontal system's approach and passage. Mis-timed prediction of a frontal system's movement is also found to contribute to the air quality model's bias in simulation of local/regional air pollutants.