A comparative study of PM2.5 ambient aerosol chemical databases

Comparing PM2.5 chemical databases at different sites and times is of interest in developing air quality control strategies, planning health effects studies, and "harmonizing" international standards. Three methods of comparison were applied to databases for the fine aerosol from seven sites around the world, five urban and two nonurban. The most extensive database, for Los Angeles, was used as a reference. log-log plots of chemical concentrations at pairs of sampling sites provide an easily visualized comparison that can be characterized by the coefficient of divergence (CD) which approaches zero for similar sites and one if the sites are very different. Sites similar and dissimilar to downtown Los Angeles were Teplice (Czech Republic) and Taipei(Taiwan), respectively. Cluster analysis was used to group sampling sites with similar characteristics. The Los Angeles, Philadelphia, and Amazon Basin sampling sites each clustered strongly; Teplice fused with the Los Angeles cluster. Correlation coefficients for the spatial variation of the chemical components for aerosol sources provide a measure of source similarities for the Los Angeles sites. Differences in chemical component concentrations at different sites are caused not only by true chemical variations but also, by sampling and measurement artifacts. There is a need for intercomparison and calibration to reduce such effects.