PM chemical characterization at a semi-arid urban environment in Central Mexico

The central part of Mexico, a semi-arid region, hosts many anthropogenic activities that might affect the air quality of the several large cities within; however, the processes that occur in its atmosphere are poorly understood. Here, we investigated the concentration and chemical composition of the particulate matter in the Metropolitan Area of Queretaro for one year, together with meteorological variables and other pollutants data. Seasonal concentrations were determined mainly by meteorology. The secondary components comprised the largest fraction of PM2.5, followed by resuspension and the typical primary combustion sources in an urban area. Regional processing played a very important role in the formation of secondary aerosols. Local oxidation producing nitrate and less oxidized organic aerosols occurred more rapidly at night, although photochemical production in the morning was also observed. These results represent the first report of long-term real-time chemical characterization with high time resolution in the region. In addition, they might be important for better understanding the production of secondary aerosols in other semi-arid urban areas. [Display omitted] •All species measured showed a seasonal difference.•Most of the species measured showed higher concentrations between December and February.•60% of the particulate matter mass was of secondary origin.•Aged aerosol, probably regionally processed, comprised 44% of the particulate matter mass.•Night production of nitrate and less oxidized organic aerosol was observed.