| 20 Feb 2026
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 (OPDTT m) and a cell-based assay employing 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H2DCFDA) with alveolar epithelial cells (OPDCFH 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. OPDCFH m was correlated strongly with carbonaceous components derived from fuel combustion and transition metals (Cu, Mn, and Fe), whereas OPDTT 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, OPDTT m and OPDCFH m were correlated strongly (r = 0.81), indicating that DTT reactivity can reasonably predict cellular ROS-generating capacity of anthropogenic fine particles.
The submitted manuscript presents a study dealing with the effect of transboundary transport from continental Asia and local emissions on the oxidative potential OP) of fine particles at urban and rural sites in Japan. The OP was evaluated using a cell-free dithiothreitol (DTT) assay and an alveolar epithelial cell-based dichlorofluorescin diacetate assay.
The results are interesting and of high quality. The paper will provide more insights into the impact of different pollution sources on the different pathways for reactive oxygen species (ROS) generation in the two employed assays. However, there are a few issues that need to be addressed before accepting the paper for publication in ACP. Major revisions of the paper, taking into consideration the comments reported below, are requested.
Specific comments:
Table 1: Recalculate the mass of the collected sample to the average mass concentration of PM2.5 during the sampling periods and compare it with the corresponding data from nearby monitoring stations. Data from monitoring stations provide also as average concentrations. Give all results to 3 valid digits.
Lines 144-154: The procedure used to measure OPDCFH differs from similar papers; in particular, there is no positive control using zymosan. The authors should discuss the reasons for their choice in detail. The relative percentages used as the unit for OPDCFH measurement then prevent direct comparison with other papers.
Lines 220-225: The difference in the contribution from transboundary transport from continental Asia and local anthropogenic emissions to observed both OPDTT and OPDCFH was more significant than seasonal variations. Could you, therefore, quantify the difference in the contribution from transboundary transport and local anthropogenic emissions to OPDTT and OPDCFH at all sites studied?
Lines 281-315: Expression of the concentration of particulate component as a mass fraction (%) is unusual and prevents direct comparison of results with other studies. It is appropriate to replace the mass fraction (%) with commonly used units (i.e., ng/m3, ug/m3) or, at least, express the concentration in both ways in parallel.
Lines 321-322: K+ serves as an indicator of biomass burning, not coal combustion.
Lines 363-372: It is known that transition metals, quinones and many other particulate components contribute significantly to ROS generation. In this study, only transition metals were analysed. Why did you not also analyse quinones and other organic compounds that are known to contribute to ROS production?
Trivial mistakes:
Line 126: Correct KHPO4 to KH2PO4
Line 379: Correct Fig. 6 to Fig. 7