Institute of Urban Meteorology, China Meteorology Administration, Beijing 100089, China.
State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China; Institute of Urban Meteorology, China Meteorology Administration, Beijing 100089, China.
Sci Total Environ. 2020 May 10;716:137074. doi: 10.1016/j.scitotenv.2020.137074. Epub 2020 Feb 1.
Hygroscopicity is an important property of aerosols, which cannot be obtained for a wide range of particle sizes by online observation. A cascade impactor sampler, an essential method for obtaining the size-resolved chemical compositions of ambient aerosols, enables the acquisition of the size-resolved hygroscopicity for particles in multiple modes. A micro-orifice uniform deposit impactor (MOUDI-122, MSP) was used to collect the size-resolved aerosol samples during 2016 and 2017. The water-soluble components in these samples were analysed for different pollution levels in two periods. Then, the hygroscopicity parameter (κ) was calculated. The changing hygroscopicity in different size ranges was directly influenced by variations in the distribution of the water-soluble components. The contribution of sulfate to the κ was much higher in the summer period than that in the winter period due to the higher SO concentration in the summer. During the summer period, the contribution of nitrate to the κ of particle sizes above 0.56 μm was significantly higher than that of particles smaller than 0.56 μm, while in the winter period, the contribution of nitrate in finer particles with sizes below 1.8 μm was much higher than that in coarse particles. The contribution of chloride to the κ increased significantly in the winter period due to the influence of heating coal emissions. For particles below 1.0 μm, the contribution and fraction of water-soluble organic compounds (WSOCs) to the aerosol hygroscopicity increased with decreasing particle size. Compared with the aerosol hygroscopicity during the first stage of a pollution episode, the hygroscopicity of particles above 0.18 μm was significantly enhanced during the stages of pollution accumulation and formation. The results in this study were in good agreement with the results of other similar studies or data derived by other methods, indicating that the hygroscopicity based on size-resolved water-soluble components is reliable and can be used in the study of activation, radiation force, and heterogeneous reaction mechanism of particles with multiple sizes.
吸湿性是气溶胶的一个重要特性，而对于广泛的粒径范围，无法通过在线观测获得。级联冲击采样器是获取环境气溶胶粒径分辨化学成分的基本方法，它能够以多种模式获取多个粒径范围的粒子的粒径分辨吸湿性。在 2016 年和 2017 年，使用微通道气流分级撞击器（MOUDI-122，MSP）来收集粒径分辨气溶胶样品。在两个时期，对这些样品中的水溶性成分进行了不同污染水平的分析，然后计算了吸湿性参数（κ）。不同粒径范围内吸湿性的变化直接受到水溶性成分分布变化的影响。由于夏季 SO浓度较高，硫酸盐对夏季 κ 的贡献远高于冬季。在夏季，硝酸盐对粒径大于 0.56μm 的颗粒 κ 的贡献明显高于粒径小于 0.56μm 的颗粒，而在冬季，细颗粒（粒径小于 1.8μm）中的硝酸盐贡献远高于粗颗粒。由于供暖煤炭排放的影响，冬季氯对 κ 的贡献明显增加。对于小于 1.0μm 的颗粒，水溶性有机化合物（WSOCs）对气溶胶吸湿性的贡献和分数随着颗粒尺寸的减小而增加。与污染事件第一阶段的气溶胶吸湿性相比，在污染积累和形成阶段，粒径大于 0.18μm 的颗粒的吸湿性显著增强。本研究的结果与其他类似研究或其他方法得出的数据的结果一致，表明基于粒径分辨水溶性成分的吸湿性是可靠的，可以用于研究不同粒径颗粒的激活、辐射力和多相反应机制。
