Contribution of Soil, Sulfate, and Biomass Burning Sources to the Elemental Composition of PM10 from Mexico City

This study is aimed to identify sources of particulate matter with mean aerodynamic diameter below 10 µm (PM10) present in the atmosphere of the Metropolitan Area of Mexico City (MAMC), using samples obtained from January 1st to June 30th, 2009, analyzed with X-ray spectrometric techniques. MiniVol samplers were used to collect samples on polycarbonate filters in three sites (North, Center, and South) of the MAMC. The filters were exposed along 24 h every two days, starting at 8:00 AM, and then analyzed with particle induced X-ray emission (PIXE), a microPIXE (µPIXE) system, and X-ray fluorescence (XRF). Statistical multivariate tests with positive matrix factorization (PMF) were conducted to identify possible contributing factors. The model HYSPLIT was used to determine back-trajectories and the MODIS database for fire spot localization. The multivariate methods identified five factors in the Center and South, and four in the North, including Soil, Sulfate, Fuel/Industry, and Biomass burning, with certain differences in the factors and contributions. Application of HYSPLIT back-trajectories associated these factors to three main Soil sources and points of secondary aerosols production, as well as locations where Biomass burning aerosols were originated. The combination of X-ray spectrometric methods, receptor modeling, back-trajectory determination, and fire site localization, allowed the identification of possible sources of PM10 in the MAMC, namely, the dry Texcoco lake, the Toluca Valley, and the North dry plains for Soil aerosols, the influence of local industrial areas for Sulfate (secondary) aerosols, and the appearance of fires for Biomass burning.