Atmospheric Dry and Lead Deposition in an Arid Mexican City: Legacy of Smelting and Leaded Gasoline.

Torreón, located in central-northern Mexico, is a semiarid, dusty city affected by particulate matter and lead (Pb) pollution. This pollution is largely driven by the Met-Mex Peñoles smelting and refining complex (operating since 1901), one of the largest Ag–Cd–Pb–Zn facilities in the world, as well as historical leaded gasoline combustion (1920s–1997). In this study, we focus on atmospheric dry and lead deposition measurements in the urban area in Torreón. Atmospheric dry deposits (ADD) were collected under typical climatic conditions between January and May in 2015 and 2017. Atmospheric dry deposition fluxes (ADDF, g m2 d−1) and Pb dry deposition fluxes (Pb-DDF, mg m2 d−1) were quantified using high-resolution magnetic sector mass spectrometry. ADDF ranged from 1.0 to 1.7 g m2 d−1 near the smelter stack during windy periods to below 0.1 g m−2 d−1 at more distant locations (> 3 km) during clean days. Corresponding Pb-DDF varied from < 0.1 to 0.82–1.16 mg m2 d−1. Two dust storm events in April 2017, typical of the region, caused ADDF and Pb-loads to increase by 82 times and 67 times, respectively, compared to days with good air quality. ADDF and Pb-DDF decreased with distance from the smelting complex, with the highest concentrations found within 1 km to the west and east of the smelter, along the Sierra de las Noas hill. This hill acts as a physical barrier, restricting the dispersion of metal-rich particles, thus exacerbating urban pollution. Metal-rich particles from legacy smelter operations and leaded gasoline remain in Torreón’s urban environment.