Nitrate transboundary heavy pollution over East Asia in winter
Nitrate transboundary heavy pollution over East Asia in winter
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DOI：
10.5194/acp-17-3823-2017
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发表时间：
2017-03-20
影响因子：
6.3
通讯作者：
Kanaya, Yugo
中科院分区：
文献类型：
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作者：
Itahashi, Syuichi;Uno, Itsushi;Kanaya, Yugo
2015年1月在日本西部福冈（北纬33.52度，东经130.47度）进行的密集观测活动中，两次观测到约100 mu gm（3）的高PM2.5浓度。利用区域化学输送模式和地面观测数据，结合能捕捉到二次无机气溶胶（SO 42-、NO3-和NH 4+）行为的先进测量系统，对这些事件进行了综合分析，发现第一次PM2. 5高浓度事件以NO3-（N型）为主，第二次以SO 42-（S型）为主。NH 4+（SO 42-和NO3-的平衡离子）浓度在两种类型中均较高。化学迁移模型中的敏感性模拟表明，这两种类型的污染主要来自跨界空气污染。为了进一步研究这些类型之间的差异，对化学传输模型的结果进行了检查，并使用了后向轨迹分析来提供额外的信息。在这两种类型的事件，高浓度的NO3-被发现在中国上空，和一个空气团，来自中国东北地区到达福冈。从中国海岸线到福冈的旅行时间因类型而异：N型为18 h，S型为24 h。随着气团靠近福冈，N型的SO2转化为SO 42-（F-s）的比例小于0.1，而S型的转化为SO 42-（F-s）的比例达到0.3。S型的较高F-s与较高的相对湿度和产生H2 O2的HO 2浓度有关，H2 O2是水相产生SO 42-的最有效氧化剂。分析NO3-对SO 42-和NH 4+变化的敏感性，结果表明，中国上空N型大气为富NH3，而S型大气基本为中性。因此，虽然中国上空的高浓度NO3-在从中国到福冈的输送过程中逐渐下降，但由于N型的SO 42-较低，因此在输送过程中NO3-浓度较高。而S型则相反，SO 42-的产生导致NH 4 NO3的分解，并使更多的SO 42-被迁移。值得注意的是，N型输送模式仅限于日本西部，特别是九州岛。以SO 42-（S型）为主的跨界空气污染已被认为是东亚地区的主要污染模式。然而，我们的研究证实了以NO3-为主的跨界空气污染的重要性，这将有助于我们更好地了解东亚冬季跨界重PM2.5污染。
High PM2.5 concentrations of around 100 mu gm(3) were observed twice during an intensive observation campaign in January 2015 at Fukuoka (33.52 degrees N, 130.47 degrees 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-(F-s) was less than 0.1 for type N, but reached 0.3 for type S as the air mass approached Fukuoka. The higher F-s 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.