PIXE analysis of atmospheric aerosols in Mexico City

Samples of atmospheric aerosols were collected at three sites in the metropolitan area of Mexico City and analyzed with particle-induced x-ray emission (PIXE). Stacked filter units of the Davis design were employed to obtain samples of PM 15 (particles with dimensions below 15 μm mean aerodynamic diameter) on polycarbonate filters, divided in two fractions. The study was conducted during the first half of 2002, exposing the filters every 2 days for 24 h, starting at 08:00 h. Analysis of variance of the measured elemental concentrations showed differences in the mean concentrations for several elements at the sampling sites. Cluster and absolute principal component analyses were applied to identify contributing sources, together with their relative contributions to the mass measured with PIXE. It was found that fugitive dusts are usually the main sources in both fractions from all sites.