Source apportionment of PM2.5 and its oxidative potential in inland and coastal areas in Japan using positive matrix factorization with composite extraction

Abstract

Fine particulate matter with a diameter ≤2.5 μm (PM_2.5) can penetrate the respiratory system and generate reactive oxygen species (ROS), posing a threat to human health. The ability to generate ROS can be represented by the oxidative potential (OP) of PM_2.5 in air. Herein, PM_2.5 was collected from Kyoto and Suzu, Japan, which are downwind regions in East Asia. Kyoto represents a typical densely populated urban center situated in one of Japan's plains, and Suzu is a remote coastal town. This pairing provides a representative framework for assessing OP-related health risks across different environmental settings in Japan. Composite extraction using water and methanol as solvents was used to extract the chemical components of samples, and the OP values of their water-soluble (OP_Ws-DTT) and methanol-soluble (OP_Ms-DTT) fractions were assessed via dithiothreitol (DTT) assay. The daily average of the total DTT consumption rate (OP_Ws-DTT + OP_Ms-DTT) was 436.8 ± 249.7 pmol/min/m³ in Kyoto and 141.0 ± 54.0 pmol/min/m³ in Suzu. The OP_Ms-DTT/OP_Ws-DTT ratio exceeded 30 % in both locations, indicating that methanol could effectively complement water in estimating the OP of PM_2.5. Positive matrix factorization analysis revealed seven pollution sources in Kyoto and six in Suzu. Biomass burning and secondary sulfate with soil were the main OP contributors in both locations. Kyoto (inland) and Suzu (coastal) were both influenced by marine aerosols. Additionally, transboundary pollution from northeast Asia was observed in Suzu. These results highlight significant differences in the OP-relevant PM_2.5 sources between locations and the variable, non-negligible contribution of water-insoluble components.