Source apportionment of water-soluble oxidative potential in ambient total suspended particulate from Bangkok: Biomass burning versus fossil fuel combustion

Abstract

Abstract Oxidative potential (OP) is a promising and integrative metric for assessing health effects associated with exposure to ambient particulate matter. Source apportionment of water-soluble OP in aerosols is the basis for formulating pollution control policies. In this study, we collected total suspended particulate (TSP) samples in Bangkok, on the Indochinese Peninsula, where pollution levels are high due to annual biomass burning. We analyzed the chemical composition of the samples and performed dithiothreitol (DTT) assays to measure their OP. We observed higher TSP mass and chemical species concentrations among samples collected in the dry seasons due to biomass burning and fossil fuel combustion. The seasonally averaged volume-normalized OP (OPv) was highest in the dry I season (January to March), which was consistent with higher TSP concentrations during this period. The mass-normalized OP (OPm) decreased as TSP concentration increased due to the unaccounted fractions dominating the increase in TSP and/or the inhibiting effects of redox-active metals. Transition metals (e.g., Cu, V, and Ni), hopanes/steranes, and carbonaceous species (organic carbon and elemental carbon) correlated well with OPm. Source apportionment using the Positive Matrix Factorization model (PMF) and multiple linear regression analysis revealed that, although biomass burning accounted for the highest contribution (mean: 26%) to TSP concentration, the dominant source of water-soluble OPv of TSP was fossil fuel combustion, which included land fossil fuel combustion (63%) and ship emissions (16%). This significant contribution of fossil fuel combustion was determined by the transition metals Cu and V which were the main drivers of DTT activity in TSP.