Atmospheric pollution derived from PM2.5 particles produced in fireworks burning events in Mexico City

Fireworks (FW) burnings have attracted the attention of the scientific community because of the potential risks they pose to the environment and human health. In the Mexico City Metropolitan Area (MCMA) and in its surroundings, FW burnings are displayed during local celebrations, depositing large amounts of smoke and fine particles into the atmosphere. That is the case of Christmas and New Year’s Eve celebrations, when FW are sequentially displayed in many countries around the world according to their time zones, causing a global effect. In this study, PM_2.5 samples were collected simultaneously from seven strategic sampling sites in the MCMA during Christmas and New Year’s Eve from 2005 to 2010, when FW burning events occurred, and most of the mass concentrations exceeded by a factor of 2–3 times the Mexican Air Quality Standard (NOM) of 65 μg/m³ in 24 h (value level at the time of sampling). A set of 77 samples were analyzed by Particle induced X-ray emission (PIXE) to determine their elemental concentrations. Fifteen elements (S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, As, Br, Ba, Pb) were identified in the samples, six of them (Cl, K, Ca, Cr, Cu, Ba) with high concentrations in comparison to samples collected during normal days, when no pyrotechnics were displayed. Ba was found with very high concentrations during these events in comparison with ordinary days, when it barely reached its minimum detection limit. So, it was recognized as the best FW tracer for this study. Several pairs of elements showed good correlations in most of the years under study, which allowed us to infer the presence of some characteristic chemical compounds of the gunpowder used locally.