Liu Zirui, Xie Yuzhu, Hu Bo, Wen Tianxue, Xin Jinyuan, Li Xingru, Wang Yuesi
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China.
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China.
Chemosphere. 2017 Sep;183:119-131. doi: 10.1016/j.chemosphere.2017.05.095. Epub 2017 May 17.
Size-segregated water-soluble ionic species (WSIs) were measured using an Anderson cascade impactor from Jul. to Aug. 2008 and from Dec. 2009 to Feb. 2010 in urban Beijing. The results showed that fine particles (PM, Dp < 2.1 μm) accounted for ∼49% (summer) and ∼34% (winter) of the total particulate mass, and WSIs accounted for 23-82% of the mass concentration of PM. Secondary inorganic aerosols (SIAs, the sum of SO, NO and NH) accounted for more than 30% of the fine particles, which were greatly elevated during particle pollution events (PM events), thereby leading to an alteration of the size distributions of SO and NO to nearly single fine-mode distributions peaking at 0.65-2.1 μm. This finding suggests that heterogeneous aqueous reactions were enhanced at high RH values. SIAs also increased during dust events, particularly for coarse mode SO, which indicated enhanced heterogeneous reactions on the dust surface. The positive matrix factorization (PMF) model was used to resolve the bulk mass size distributions into condensation, droplet, and coarse modes, representing the three major sources of the particles. The formation of SO was attributed primarily to in-cloud or aerosol droplet processes during summer (45%), and the heterogeneous reaction of SO on mineral dust surfaces was an important formation pathway during winter (45%). The formation pathways of NO in fine particles were similar to those of SO, where over 30% were formed by in-cloud processes. This work provides important field measurement-based evidence for understanding the formation pathway of secondary inorganic aerosols in the megacity of Beijing.
2008年7月至8月以及2009年12月至2010年2月期间，在北京城区使用安德森级联撞击器对按粒径分级的水溶性离子物种（WSIs）进行了测量。结果表明，细颗粒物（PM，空气动力学直径Dp < 2.1μm）占总颗粒物质量的约49%（夏季）和约34%（冬季），而WSIs占PM质量浓度的23 - 82%。二次无机气溶胶（SIAs，SO₄²⁻、NO₃⁻和NH₄⁺的总和）占细颗粒物的比例超过30%，在颗粒物污染事件（PM事件）期间大幅升高，从而导致SO₄²⁻和NO₃⁻的粒径分布改变为几乎单一的细模态分布，峰值出现在0.65 - 2.1μm。这一发现表明，在高相对湿度值下非均相水相反应增强。在沙尘事件期间SIAs也有所增加，特别是粗模态的SO₄²⁻，这表明沙尘表面的非均相反应增强。采用正矩阵因子分解（PMF）模型将总质量粒径分布解析为凝结核模态、液滴模态和粗模态，分别代表颗粒物的三个主要来源。SO₄²⁻的形成主要归因于夏季云内或气溶胶液滴过程（45%），而冬季SO₄²⁻在矿物粉尘表面的非均相反应是重要的形成途径（45%）。细颗粒物中NO₃⁻的形成途径与SO₄²⁻相似，其中超过30%是通过云内过程形成的。这项工作为理解北京这个特大城市中二次无机气溶胶的形成途径提供了重要的基于现场测量的证据。
