Oxidative potential of fine particles at urban and rural sites in eastern and western Japan: effects of transboundary transport from continental Asia and local emissions

Abstract. Oxidative stress is a key mechanism that contributes to the toxicity of atmospheric aerosol particles. We investigated the mass-normalized oxidative potential (OP) of fine particles collected at three sites in Japan: Yokohama (an urban background site in the Greater Tokyo Area), Fukuoka (an urban background site in western Japan), and Noto (a rural site on the Noto Peninsula facing the Sea of Japan). The OP was evaluated using two assays: a cell-free dithiothreitol (DTT) assay (OPmDTT) and a cell-based assay employing 5-(and-6)-chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H2DCFDA) with alveolar epithelial cells (OPmDCFH). Both OP metrics exhibited significant spatial variation, with the highest values in Yokohama, followed by those in Fukuoka and Noto. This spatial pattern suggests that fine particles influenced by local urban emissions have higher intrinsic OP than those affected by long-range transport from continental Asia. Secondary particle formation during atmospheric transport likely alters the chemical composition of the particles, providing a plausible explanation for the lower intrinsic OP compared to locally emitted urban aerosol particles. OPmDCFH was correlated with carbonaceous components derived from fuel combustion and transition metals (Cu, Mn, and Fe) (r=0.47–0.84), whereas OPmDTT was associated mainly with the transition metals (r=0.67–0.82). These results indicate different pathways for reactive oxygen species (ROS) generation in the two assays. Despite these differences, OPmDTT and OPmDCFH were positively correlated (r=0.81), indicating that DTT reactivity can reasonably predict the anthropogenic fine particle-induced increase in intracellular oxidative activity.