Carbonaceous fraction in PM2.5 of six Latin American cities: Seasonal variations, sources and secondary organic carbon contribution.

Latin American (LatAm) cities are grappling with elevated levels of gaseous and particulate pollutants, which are having detrimental effects on both the local ecosystem and human health. Of particular concern are aerosols with smaller diameters (lower or equal to 2.5 µm, PM2.5), known for their ability to penetrate deep into the respiratory system. While measurements in the region are increasing, they remain limited. This study addresses this gap by presenting the results of a comprehensive, year-long PM2.5 monitoring campaign conducted in six LatAm cities: Buenos Aires, São Paulo, Medellín, San José, Quito and Ciudad de México. Despite all six monitoring sites being urban, they exhibited significant variations in PM2.5 levels, as well as in the content and seasonal behavior of elemental carbon (EC) and organic carbon (OC). Estimations of secondary organic carbon (SOC) using the EC-tracer method revealed a notable SOC relevance across all cities: secondary organic aerosols (SOA) accounted in average for between 19 % to 48 % of the total carbonaceous matter. Source attribution, conducted through the Positive Matrix Factorization (PMF) model, highlights substantial contributions from gasoline and diesel traffic emissions (29 % to 49 % of total carbon, TC), regional biomass burning (21 % to 27 %), and SOA (20 % to 38 %) in all cities, with similar chemical signatures. Additionally, industrial emissions were significant in two cities (Medellín and San José), while two others experienced minor impacts from construction machinery at nearby sites (Buenos Aires and Quito). This comparative analysis underscores the importance of considering not only the thermal optical EC/OC fractions as tracers of sources but also the OC/EC ratio of the PMF factors. This dual approach not only adds depth to the research but also suggests varied methodologies for addressing this crucial environmental concern. This study lays the groundwork for future investigations into the factors influencing the content and seasonality of SOA in the region.