Transboundary Transport of Nitrogen Oxides from the Asian Continent to Fukue Island, Japan: Analyses of Long-Range Transport of Nitrogen Compounds

ABSTRACTTo investigate long-range transport and oxidation states of nitrogen compounds from the Asian continent, especially of total odd nitrogen species (NOy), we carried out continuous observations of NOy, total nitrate (T.NO3; the sum of gaseous nitric acid and particulate nitrate) and NOx (= NO + NO2) at Fukue Island, located in westernmost Japan. NOy and T.NO3 exhibited similar seasonal cycles, with maximum concentrations observed during winter-spring seasons, and minimum concentrations during summer. NOx had a seasonal cycle, with maximum and minimum concentrations in winter and summer, respectively; NOx concentrations also decreased markedly from winter to spring. High-concentration event analyses to assess transboundary pollution of NOy were performed. Transboundary pollution events for NOy were extracted, and classified as either “Case 1” or “Case 2”. Case 1 involved transport of NOy, T.NO3, and NOx from the Asian continent to Fukue Island, while Case 2 involved transport of NOy and T.NO3, but not NOx. Case 1 and Case 2 occurred predominantly in winter and spring, respectively. Air mass trajectories indicated that in Case 1, 52% of air masses passed through Korea, while only 5% passed through Korea in Case 2. These results indicate that some NOx emitted from the Asian continent is transported to Fukue Island as NOx, without it undergoing oxidation, reflecting low photochemical activity and/or short transport times.