Seasonal evaluation of sulfur species identified in PM2.5 obtained in Monterrey, Mexico

This work studies the elemental seasonal variation in the PM_2.5 obtained from the Monterrey Metropolitan Area with particular emphasis on sulfur species. The existence of these sulfur species was identified in all samples analyzed in this work. The results of this work evidence the formation of surface layers rich in sulfur compounds, which indicates the formation of secondary organic aerosols. This point was confirmed by the highest correlation identified between O₃ concentration and relative humidity with the sulfur wt% in PM_2.5. Additionally, this work proposes a multiple-liner correlation among sulfur wt% formed on PM_2.5 with several pollutants and meteorological conditions, identifying the main contributors to their formation. Results suggest first the formation of sulfite species followed by their oxidation to sulfate species, which are promoted by specific conditions of relative humidity and O₃. Among all evaluated seasons, samples obtained in fall showed the highest amount of sulfur wt% attributable to a synergetic effect between relative humidity and O₃ concentration.