Key Laboratory of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai 200241, China.
Institute of Mass Spectrometer and Atmospheric Environment, Jinan University, Guangzhou 510632, China.
Sci Total Environ. 2021 Feb 25;757:143741. doi: 10.1016/j.scitotenv.2020.143741. Epub 2020 Nov 26.
The diacid chemistry of summertime PM and the size-segregated aerosols (9-stages) in Chongming Island, a coastal site in the Yangtze River Delta (YRD), China, were investigated. Our results showed that oxalic acid (C) was the dominant dicarboxylic acid, followed by succinic acid (C), malonic acid (C), adipic acid (C) and phthalic acid (Ph). Two types of haze pollution events were identified during the sampling period, i.e., Event I, which was mainly caused by the local biomass burning emission, and Event II, which was caused by a long-distance transport of the YRD urban pollution. C linearly correlated with SO and NO in Event I but only with O in Event II, indicating that oxalic acid formation was dominated by the aerosol aqueous phase oxidation in Event I and by the gaseous phase oxidation in Event II, respectively. 65.5% of Cl in sea salts at the site in the clean period was depleted and robustly correlated with oxalic acid (R = 0.74). We proposed a mechanism to explain such a significant Cl depletion, in which anthropogenic VOC oxidize into oxalic acid and its precursors such as glyoxal and methyglyoxal by a photochemical oxidation, and then oxalic acid and the related compounds subsequently react with sea salts and release HCl into the troposphere. The significant Cl depletion of sea salts related with the organic acid (C) in coastal China was found for the first time and should be considered in future studies, because oxalic acid and related SOA in the country are abundant and the released HCl may effectively enhance the oxidation capacity of the atmosphere by photolytically producing Cl radicals.
研究了中国长江三角洲（YRD）沿海岛屿崇明岛夏季 PM 和分段采集的气溶胶（9 级）中的二酸化学。结果表明，草酸（C）是主要的二羧酸，其次是琥珀酸（C）、丙二酸（C）、己二酸（C）和邻苯二甲酸（Ph）。在采样期间确定了两种类型的霾污染事件，即事件 I，主要由当地生物质燃烧排放引起，和事件 II，由 YRD 城市污染的长距离传输引起。在事件 I 中，C 与 SO 和 NO 呈线性相关，但在事件 II 中仅与 O 相关，表明草酸的形成分别由事件 I 中的气溶胶水相氧化和事件 II 中的气相氧化主导。在清洁期，现场海盐中 65.5%的 Cl 被消耗，与草酸（R=0.74）呈强相关。我们提出了一种机制来解释这种明显的 Cl 消耗，其中人为 VOC 通过光化学氧化转化为草酸及其前体，如乙二醛和甲基乙二醛，然后草酸和相关化合物与海盐反应并将 HCl 释放到对流层。在中国沿海首次发现与有机酸（C）相关的海盐明显 Cl 消耗，在未来研究中应予以考虑，因为该国的草酸和相关 SOA 很丰富，释放的 HCl 可能通过光解产生 Cl 自由基有效增强大气的氧化能力。
