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.