Relationship of PM fine to ozone and meteorology

In this study, the authors have analyzed the ambient PM2.5 concentration data collected in the US during the period between 1988 and 1993 to examine the relationship of PM fine episodes to ozone and meteorology. The data base includes AIRS data, IMPROVE data, and the California special monitoring data. To minimize the influence of different data collection methods and to allow a fair comparison between urban and rural episodes, they have used a normalization technique of applying temporal data distribution parameters to select PM2.5 episodes. Among the 81 selected regional PM2.5 episode days more than half (46) of them occurred in the summer. The synoptic analysis results suggest that PM2.5 episodes are essentially associated with the summertime stagnant high pressure systems in most parts of the United States except for California. In California, the influence of cold season stagnant high pressure systems and topographic trapping of pollutants are the key triggering mechanisms for regional PM2.5 episodes. While the PM2.5 episodes and ozone episodes are so closely related in the eastern United States, they are almost totally decoupled in California. This is confirmed by the regression analyses of PM2.5 versus ozone and meteorology which show that ozone is the best predictormore » for PM2.5 in the East but not even close to being a significant predictor in California. Both the synoptic and regression analyses suggest that pollutant transport (as revealed in the wind speed and direction) is much more important to high PM2.5 concentrations in the East than in the West. The episodic relationship of PM2.5 and meteorology are analyzed using a spline function to fit through the 99th percentile of all paired PM2.5-meteorology data in a region.« less