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 contribute to the toxicity of atmospheric aerosol particles. This study 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 (OP^DTT _m) and a cell-based assay employing 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H₂DCFDA) with alveolar epithelial cells (OP^DCFH _m). 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 those of locally emitted urban aerosol particles.  OP^DCFH _m was correlated strongly with carbonaceous components derived from fuel combustion and transition metals (Cu, Mn, and Fe), whereas OP^DTT _m was associated mainly with the transition metals. These results indicate different pathways for reactive oxygen species (ROS) generation in the two assays. Despite these differences, OP^DTT _m and OP^DCFH _m were correlated strongly (r = 0.81), indicating that DTT reactivity can reasonably predict cellular ROS-generating capacity of anthropogenic fine particles.