ELEMENTAL COMPOSITION AND SOURCE IDENTIFICATION OF PM2.5 PARTICLES COLLECTED IN DOWNTOWN MEXICO CITY

Fine particulate matter PM2.5 samples have been regularly collected in the Mexico City Metropolitan Area commencing in the year 2003, when a new PM2.5 sampling network was made fully operational. Samples have been collected during 24 h periods every third day using US EPA Federal Reference Method (FRM) samplers. In this study, the elemental composition of two sets of PM2.5 samples collected at the "Merced" sampling site located in downtown Mexico City (19°25'28''N, 99°07'09''W) were determined by PIXE. Ten elements (S, Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, and Pb) were detected in most of the samples. Some others appeared occasionally, but only those consistently detected were considered significant for the analysis. Other analytical equipments operating simultaneously at the site provided complementary data of several variables such as SO2, NO2, NOx and CO. An enhanced database was thus built adding these results to the database derived from previous PIXE analysis. Further statistical analysis of the database allowed identifying four principal sources in two seasons and permitted to estimate the corresponding source apportionment.