Articles | Volume 17, issue 6
Atmos. Chem. Phys., 17, 3823–3843, 2017

Special issue: Global and regional assessment of intercontinental transport...

Atmos. Chem. Phys., 17, 3823–3843, 2017

Research article 20 Mar 2017

Research article | 20 Mar 2017

Nitrate transboundary heavy pollution over East Asia in winter

Syuichi Itahashi1, Itsushi Uno2, Kazuo Osada3, Yusuke Kamiguchi3,a, Shigekazu Yamamoto4, Kei Tamura5, Zhe Wang2,6, Yasunori Kurosaki7, and Yugo Kanaya8 Syuichi Itahashi et al.
  • 1Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba 270-1194, Japan
  • 2Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga Park, Kasuga, Fukuoka 816-8580, Japan
  • 3Graduate School of Environmental Studies, Nagoya University, D2-1 (510) Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
  • 4Fukuoka Institute of Health and Environmental Sciences, 39 Mukaizano, Dazaifu-shi, Fukuoka 818-0135, Japan
  • 5Nagasaki Prefectural Environmental Affairs Department, 2-1306-11 Ikeda, Omura, Nagasaki 856-0026, Japan
  • 6Institute of Atmospheric Physics, Chinese Academy of Sciences, 40 Huayanli, Chaoyang, Beijing 100029, China
  • 7Arid Land Research Center, Tottori University, 1390 Hamasaka, Tottori 680-0001, Japan
  • 8Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan
  • apresent address: JCB Co. Ltd., Tokai Regional Office, 2-16-26, Nishiki, Naka-ku, Nagoya, Aichi 460-0003, Japan

Abstract. High PM2. 5 concentrations of around 100 µg m−3 were observed twice during an intensive observation campaign in January 2015 at Fukuoka (33.52° N, 130.47° E) in western Japan. These events were analyzed comprehensively with a regional chemical transport model and synergetic ground-based observations with state-of-the-art measurement systems, which can capture the behavior of secondary inorganic aerosols (SO42−, NO3, and NH4+). The first episode of high PM2. 5 concentration was dominated by NO3 (type N) and the second episode by SO42− (type S). The concentration of NH4+ (the counterion for SO42− and NO3) was high for both types. A sensitivity simulation in the chemical transport model showed that the dominant contribution was from transboundary air pollution for both types. To investigate the differences between these types further, the chemical transport model results were examined, and a backward trajectory analysis was used to provide additional information. During both types of episodes, high concentrations of NO3 were found above China, and an air mass that originated from northeast China reached Fukuoka. The travel time from the coastline of China to Fukuoka differed between types: it was 18 h for type N and 24 h for type S. The conversion ratio of SO2 to SO42− (Fs) was less than 0.1 for type N, but reached 0.3 for type S as the air mass approached Fukuoka. The higher Fs for type S was related to the higher relative humidity and the concentration of HO2, which produces H2O2, the most effective oxidant for the aqueous-phase production of SO42−. Analyzing the gas ratio as an indicator of the sensitivity of NO3 to changes in SO42− and NH4+ showed that the air mass over China was NH3-rich for type N, but almost NH3-neutral for type S. Thus, although the high concentration of NO3 above China gradually decreased during transport from China to Fukuoka, higher NO3 concentrations were maintained during transport owing to the lower SO42− for type N. In contrast, for type S, the production of SO42− led to the decomposition of NH4NO3, and more SO42− was transported. Notably, the type N transport pattern was limited to western Japan, especially the island of Kyushu. Transboundary air pollution dominated by SO42− (type S) has been recognized as a major pattern of pollution over East Asia. However, our study confirms the importance of transboundary air pollution dominated by NO3, which will help refine our understanding of transboundary heavy PM2. 5 pollution in winter over East Asia.

Short summary
Over East Asia, the transboundary air pollution of SO42− has been recognized. The importance of the transboundary air pollution of NO3 in winter was demonstrated in this study through synergetic ground-based observations with state-of-the-art measurements of secondary inorganic aerosols (SO42−, NO3, and NH4+) and a regional chemical transport model analysis. This study will help to refine the understanding of transboundary heavy PM2.5 pollution in winter.
Final-revised paper