Differentiating the contributions of particle concentration, humidity, and hygroscopicity to aerosol light scattering at three sites in China

This study investigates the relationships between aerosol backscattering (βp), aerosol liquid water content (ALWC), and numerous influential factors [ambient humidity, particle mass concentration, particle number size distribution (PNSD), and chemical composition] using comprehensive field campaign data. The data set includes numerical aerosol properties, e.g., the βp, ALWC, aerosol hygroscopicity observed at three urban sites in China: Beijing (BJ) from 20 December 2018 to 10 February 2019, Guangzhou (GZ) from 1 November 2019 to 31 January 2020, and Nanjing (NJ) from 1 November 2020 to 31 January 2021. Notable differences in the variations of aerosol backscattering with related factors at the three sites under the same pollution conditions were also demonstrated. βp was more sensitive to aerosol hygroscopicity and mass concentration in NJ and to ambient RH in BJ. The relative contributions of these factors to βp at the three sites under different pollution conditions were quantitatively evaluated. The largest impact factor to the variability in βp changed from particle mass to ambient RH as air quality deteriorated to heavy pollution in BJ, implying that the formation of heavy pollution in BJ is dependent on high humidity. The opposite was true in NJ. In GZ, the contributions of these factors to changes in βp under different polluted conditions were similar, both dominated by aerosol PM2.5.

本研究依托综合外场观测数据，探究了气溶胶后向散射系数（aerosol backscattering，βp）、气溶胶液态水含量（aerosol liquid water content, ALWC）与多项影响因子——包括环境湿度、颗粒物质量浓度、颗粒物数谱分布（particle number size distribution, PNSD）以及化学成分——之间的关联。本数据集包含中国3个城市站点的气溶胶属性实测数值，具体涵盖βp、ALWC以及气溶胶吸湿性，三个站点的观测时段分别为：北京（BJ）站点2018年12月20日至2019年2月10日，广州（GZ）站点2019年11月1日至2020年1月31日，南京（NJ）站点2020年11月1日至2021年1月31日。研究发现，在相同污染条件下，3个站点的气溶胶后向散射系数随相关因子的变化特征存在显著差异：南京站点的βp对气溶胶吸湿性与颗粒物质量浓度更为敏感，而北京站点的βp则对环境相对湿度更为敏感。本研究定量评估了不同污染情境下，上述因子对3个站点βp变化的相对贡献。在北京站点，随着空气质量恶化至重度污染，βp变化的主导影响因子从颗粒物质量转变为环境相对湿度，这表明北京地区的重度污染形成依赖于高湿度环境；南京站点则呈现相反的变化规律。在广州站点，不同污染条件下各因子对βp变化的贡献特征较为相似，整体均以PM2.5为主导。