Oxidative potential and chemical characterization of PM2.5 in a medium-sized residential city of South Korea.

PM_2.5, defined as particulate matter less than 2.5 μm, is derived from a variety of natural and anthropogenic sources. Studies have shown that PM_2.5 adversely affects human health, causing various respiratory and cardiovascular diseases. One of the methods to assess the potential health impacts of PM_2.5 is to measure its oxidative potential, which refers to the ability of the particles to generate reactive oxygen species when inhaled into the lungs. In this study, antioxidants including ascorbic acid (AA) and reduced glutathione (GSH) as well as dithiothreitol (DTT) were used to measure the oxidative potential of PM_2.5 collected in Chuncheon, a medium-sized residential city of South Korea. The degree of oxidation of antioxidants and DTT were measured using a spectrophotometric assay. In addition, a detailed PM_2.5 compositions including NO₃^-, SO₄^2-, NH₄⁺, organic carbon (OC), elemental carbon (EC), metallic elements, and individual organic substances were measured to identify the characteristics of high PM_2.5 concentration episodes (HCE) and to determine the association between chemical components with oxidative potential.

PM_2.5 concentrations were generally higher in fall than in summer, and OC was the biggest contributor to PM_2.5 mass. Among organic matters, sugar compounds, the marker species of biomass burning, were prominent while dicarboxylic acids, predominantly secondarily formed in atmosphere, were important in summer. For HCEs, NO₃^- and dicarboxylic acids increased the most among PM_2.5 components, suggesting that secondary formation was important to enhance PM_2.5 concentration. Nitrogen oxidation ratio (NOR) also increased during HCEs, and there was statistically significant correlation between NO₂ and NO₃^-, possibly indicating that in situ oxidation of NO₂ and/or gas-aerosol partitioning for HNO₃ and NO₃^- occurred. Average OP measured by depletion of AA (OP_AA), GSH (OP_GSH), and DTT (OP_DTT) were 4.5 ± 1.1, 4.9 ± 1.3, and 17.7 ± 5.9 pmol min^-1 mg^-1, respectively, during summer. All three OPs were especially low for the sample obtained when Asian dust event occurred. PM_2.5 mass concentration was successfully reconstructed by EC, ∑n-Alkane, Ca²⁺, SO₄^2–, and OC from multiple linear regression while oxidative burden by GSH (OB_GSH) was explained by EC and ∑PAHs. These different results between PM_2.5 mass and OP suggest that the PM_2.5 concentration alone is not sufficient to explain the association with health effects.