Characterization of aerosol particles during a high pollution episode over Mexico City

More than 7 thousand wildfires were recorded over Mexico in 2019, affecting almost 640 thousand hectares. Most of these fires occurred during the warm-dry season generating dense smoke plumes, impacting urban areas in the central part of the Mexican plateau. From May 10 to 17, 2019, biomass burning (BB) plumes affected Mexico City (MC) and diffused across the basin, drastically reducing visibility. Due to the severity of this high atmospheric pollution (HAP) episode, the local government declared an environmental contingency, warning the population. Fine particle (PM 2.5 ) concentrations were ~ 2 times higher than the nation's air quality standards. Likewise, aerosol optical measurements indicated that visibility was mainly affected by fine aerosol particles. Electron microscopy analysis of aerosol samples obtained during the HAP days shows a high incidence of strong absorbent soot and tarballs (TB). These types of particles were simultaneously observed in MC and at the high-altitude Altzomoni Atmospheric Observatory (~ 4010 m.a.g.l.). Elemental analysis of the particles shows that the composition is dominated by sulfur and potassium, evidencing a strong influence of the BB emissions, but also suggests the presence of urban pollution from MC at the remote Altzomoni site.