Oxidative potential of ambient PM2.5 from São Paulo, Brazil: Variations, associations with chemical components and source apportionment

The article presents the Dithiothreitol-based oxidative potential (OPDTT) of PM2.5 from an urban site in São Paulo, Brazil, in relation to its chemical composition focused on organic carbon (WSOC), Humic-Like Substances (HULIS), water-soluble elements (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd and Pb), ionic species, polycyclic aromatic hydrocarbons (PAHs), and oxy- and nitro-PAH derivatives (OPAHs and NPAHs). Seasonal variations of the intrinsic (mass-normalized) oxidative potential (OPmDTT) and the extrinsic (air volume-normalized) oxidative potential (OPvDTT), as well as of targeted chemical components were investigated. Furthermore, a series of statistical analyses, including correlation, and multi linear regression (MLR) were performed to identify the most significant species contributing to the measured OPDTT. Although explaining a relatively small percentage of the OP variability (R2 = 0.389), the MLR model indicated HULIS as the major OPmDTT carrier contributing 58% on average. Two receptor modelling approaches were further employed for the source apportionment of OPvDTT (a) direct Positive Matrix Factorization (PMF), and (b) a combination of PMF of PM2.5 mass concentrations followed by Multiple Linear Regression (PMF - MLR). Both approaches yielded meaningful, although somewhat different, results with direct PMF indicating vehicular emissions as the major contributor (76.3 ± 58.3%) of OPvDTT followed by industrial emissions (16.9 ± 17.7%), and biomass burning (7.3 ± 8.6%), whereas according to the PMF-MLR approach, the main contributors to OPvDTT were biomass burning (40.7 ± 26.3%), industrial emissions (24.3 ± 22.5%), vehicular emissions (20.5 ± 15.2%), and secondary aerosol (14.5 ± 15.0%). The study provides new and additional insights on the oxidative activity of ambient PM highlighting the importance of identifying its linkage with chemical constituents and emission sources for developing air quality control strategies aiming to protect human health. [Display omitted] •Dithiothreitol oxidative potential (OPDTT) of PM2.5 was investigated in São Paulo.•OPDTT was an intrinsic property of PM2.5 related to its composition than mass.•HULIS appeared to be a significant contributor to OPmDTT.•Direct PMF indicated vehicular emissions as the major source of OPvDTT.•The PMF - MLR approach indicated biomass burning as the major source of OPvDTT.