Seasonal Variations and Chemical Drivers of the Oxidative Potential of PM2.5 in Sao Paulo, Brazil: Insights from DTT and ESR Assays
CAROLINE FERNANDA HEI WIKUATS, Thiago Nogueira, Alessandra Tammaro, Flemming Cassee, Maria de Fatima Andrade, University of São Paulo
Abstract Number: 352
Working Group: Urban Aerosols
Abstract
The oxidative potential (OP) of fine particulate matter (PM2.5) is a critical indicator of its ability to induce oxidative stress and impact human health. Despite extensive characterization of PM2.5 physicochemical properties and emission sources in São Paulo, Brazil, its toxicity remains insufficiently explored. Moreover, seasonal variations in the city, characterized by distinct wet and dry seasons, can influence PM composition and toxicological properties. This study aims to elucidate the relationship between PM composition, meteorology, and OP in São Paulo using dithiothreitol (OPDTT) and electron spin resonance (OPESR) methods. The OPDTT assay mimics in vivo superoxide radical generation, while OPESR assesses PM's capacity to generate free radicals, particularly hydroxyl radicals. We collected 24-hour PM2.5 samples in 2021 and 2022 (n = 284) near major roads, predominantly influenced by vehicular emissions, using a Partisol 2025i Sequential Air Sampler. Composition analysis was conducted via energy-dispersive X-ray fluorescence (EDXRF) and the Lab Organic Carbon-Elemental Carbon (OC-EC) Aerosol Analyzer. Our findings demonstrate significant seasonal variations (p-value ≤ 0.05), with winter samples showing 55.6% and 41.6% higher PM2.5 concentrations and OPDTT values, respectively, compared to summer. Northeast, east, and southeast winds consistently correlated with higher values for PM2.5, OPDTT, and OPESR across all seasons. Contributions from north and northwest winds during winter suggest influences from local and regional sources (e.g., biomass burning) on OP results. Since each method detects distinct PM chemical constituents (in general, DTT targets organic compounds while ESR focuses on transition metals), further analysis aims to elucidate the relationship between organics, OPDTT, metals, and OPESR. This ongoing study contributes to advancing our understanding of PM toxicity in São Paulo, emphasizing the importance of targeted mitigation strategies to protect public health in urban environments.