State Key Laboratory of Remote Sensing Science, College of Global Change and Earth System Science, Beijing Normal University, Beijing 100875, China.
Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park, MD, USA.
Sci Total Environ. 2022 Jan 10;803:150010. doi: 10.1016/j.scitotenv.2021.150010. Epub 2021 Aug 30.
This study investigates the impact of aerosol liquid water content (ALWC) and related factors, i.e., relative humidity (RH), aerosol mass concentration (PM), and aerosol hygroscopicity, on aerosol optical properties, based on field measurements made in the Pearl River Delta (PRD) region of China at the surface (1 November 2019 to 21 January 2020) and in the upper boundary layer (the 532-m Guangzhou tower from 1 February to 21 March 2020). In general, temporal variations in the ambient aerosol backscattering coefficient (β) and ALWC followed each other. However, the surface β and 532-m β had generally opposite diurnal variation patterns, caused by dramatic differences in PM and ambient RH between the surface and the upper boundary layer. The ambient 532-m RH was systematically higher than the surface RH, with the latter having a much pronounced diurnal cycle than the former. The surface PM concentration was systematically higher than the PM concentration at 532 m, and their diurnal cycle patterns were overall opposite. These dramatic differences reveal that the atmospheric variables, i.e., ambient RH and the PM concentration in the upper boundary layer, cannot be directly represented by the same variables at the surface. Vertical variability should be considered. Clear differences in the sensitivities of aerosol light scattering to ambient RH, PM, and aerosol hygroscopicity between the two levels were found and examined. Aerosol chemical composition played a minor role in causing the differences between the two levels. In particular, β was more sensitive to PM at the surface level but more to the ambient RH in the upper boundary layer. The larger contribution of aerosol loading to the variability in β at the surface implies that local emission controls can decrease β and further improve atmospheric visibility effectively at the surface during winter in the PRD region.
本研究基于中国珠江三角洲（PRD）地区的实地（2019 年 11 月 1 日至 2020 年 1 月 21 日）和上边界层（2020 年 2 月 1 日至 3 月 21 日，广州塔 532 米高处）的实地测量数据，研究了气溶胶液态水含量（ALWC）和相关因素（相对湿度（RH）、气溶胶质量浓度（PM）和气溶胶吸湿性）对气溶胶光学性质的影响。通常，环境气溶胶后向散射系数（β）和 ALWC 的时间变化相互跟随。然而，地面β和 532 米处β的日变化模式通常相反，这是由于地面和上边界层之间的 PM 和环境 RH 存在显著差异造成的。环境 532 米 RH 普遍高于地面 RH，后者的日变化周期明显长于前者。地面 PM 浓度普遍高于 532 米处的 PM 浓度，其日变化模式总体相反。这些显著差异表明，大气变量，即上边界层中的环境 RH 和 PM 浓度，不能直接代表地面上的相同变量。应该考虑垂直变化。发现并检查了两个水平之间气溶胶光散射对环境 RH、PM 和气溶胶吸湿性的敏感性的明显差异。气溶胶化学成分在造成两个水平之间的差异方面作用较小。特别是，β在地面水平上对 PM 更敏感，但在上边界层中对环境 RH 更敏感。β在表面水平上的变异性更大程度上归因于气溶胶负荷，这意味着在 PRD 地区冬季，当地排放控制可以降低β，进一步有效提高大气能见度。
