Elemental analysis of PM10 in southwest Mexico City and source apportionment using positive matrix factorization

The results of a study of the elemental concentrations in PM 10 samples collected at a site in southwest Mexico City during 2016 and 2019, are presented. The concentrations of up to 19 elements were measured with X-ray fluorescence (XRF). These analyses were complemented with ion chromatography for eight ionic species (for the samples collected in 2016). The behaviors of the gravimetric mass and elemental concentrations are described for the morning, afternoon, and night-time periods in 2019. The elemental concentrations observed in the PM 10 samples did not present significant changes as compared to those published in previous works. It was found that the gravimetric mass concentrations were always below the official standards, except during a contingency period in May 2019. The positive matrix factorization (PMF) receptor model was used to identify contaminating sources and their relative contributions to the concentrations of the detected elements. The soil-related factors were the most abundant contributors, with other components associated to traffic, biomass burning, fuel oil, secondary aerosol, and dust resuspension. The occurrence of episodes in 2019 is explained with the aid of PMF and back-trajectories, while the contingency period is due to other chemical species not detected in PM 10 with XRF. A comparison with data collected in 2005 in downtown Mexico City is also carried out, as well as with urban areas in other countries.