Chemical speciation of organic compounds and elemental compositions of PM2.5 in Mexico City: Spatial-seasonal distribution, emission sources, and formation processes

Abstract

The simultaneous study of n-alkanes, polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs, and metals in particles ≤2.5 μm (PM2.5) provided helpful information to identify pollutant emission sources in the Metropolitan Zone of Mexico Valley (MZMV). PM2.5 samples were obtained during three seasons of a year from five sampling sites simultaneously collected. The dominant sources of the species were the incomplete combustion of fossil fuel by vehicles, followed by the resuspension of geogenic material, evaporation from petrogenic sources, and emissions from the oil refining industry. The northeast (NE) of the MZMV, hosting the industrial area, exhibited the highest contribution of ΣPAHs<228 due to the high presence of diesel vehicles. The NE also showed the highest metal concentrations of geogenic origin due to its proximity to agricultural lands and the dominant wind direction from the north to the south, introducing pollutants into the Valley. Among the pollutants, 1-nitropyrene emitted from diesel combustion sources and 2-nitrofluoranthene formed in the atmosphere were found. Particles enriched with Mn + Fe + Co + Cu and Rb were emitted from agricultural lands and volcanic soil, respectively, and originated from local/peripherical soils, while particles enriched with Cr + Cs + Th were originated from geogenic sources further away from the MZMV. Cd + Pb and n-alkanes C16-C22 were emitted outside the Valley, while PAHs, nitro-PAHs, and heavier n-alkanes (C23-C33) were emitted inside the Valley. Decision-makers could use our results to develop control strategies for air pollutants from specific sources. Comparisons of hydrocarbon and metal concentrations in other cities were also made.