Abstract
Water uptake by aerosol particles alters its light-scattering characteristics significantly. However, the hygroscopicities of different aerosol particles are not the same due to their different chemical and physical properties. Such differences are explored by making use of extensive measurements concerning aerosol optical and microphysical properties made during a field experiment from December 2018 to March 2019 in Beijing. The aerosol hygroscopic growth was captured by the aerosol optical characteristics obtained from micropulse lidar, aerosol chemical composition, and aerosol particle size distribution information from ground monitoring, together with conventional meteorological measurements. Aerosol hygroscopicity behaves rather distinctly for mineral dust coarse-mode aerosol (Case I) and non-dust fine-mode aerosol (Case II) in terms of the hygroscopic enhancement factor, f β ( R H , λ 532 ) , calculated for the same humidity range. The two types of aerosols were identified by applying the polarization lidar photometer networking method (POLIPHON). The hygroscopicity for non-dust aerosol was much higher than that for dust conditions with the f β ( R H , λ 532 ) being around 1.4 and 3.1, respectively, at the relative humidity of 86% for the two cases identified in this study. To study the effect of dust particles on the hygroscopicity of the overall atmospheric aerosol, the two types of aerosols were identified and separated by applying the polarization lidar photometer networking method in Case I. The hygroscopic enhancement factor of separated non-dust fine-mode particles in Case I had been significantly strengthened, getting closer to that of the total aerosol in Case II. These results were verified by the hygroscopicity parameter, κ (Case I non-dust particles: 0.357 ± 0.024; Case II total: 0.344 ± 0.026), based on the chemical components obtained by an aerosol chemical speciation instrument, both of which showed strong hygroscopicity. It was found that non-dust fine-mode aerosol contributes more during hygroscopic growth and that non-hygroscopic mineral dust aerosol may reduce the total hygroscopicity per unit volume in Beijing.
Highlights
The presence of aerosols has an important impact on the Earth’s climate and environmental changes
Aerosol hygroscopicity is described by hygroscopic growth factor (GF), which is defined as the ratio of the wet particle diameter at a high relative humidity (RH) to that of the dry particle [8] ( Meier et al, 2009)
The first step in selecting a hygroscopic growth case is to ensure that the increase in moisture in the aerosol is accompanied by increases in aerosol optical parameters (e.g., β) and microphysical parameters
Summary
The presence of aerosols has an important impact on the Earth’s climate and environmental changes. Some researchers use fβ(RH, λ) and GF to derive κ [13,14] Most of these studies focused on the hygroscopicity of fine-mode spherical aerosol particles. A water-absorbing process has been observed to occur on the surface layer of mineral dust particles, changing their apparent morphological properties, impacting dust–cloud interactions [17]. Laboratory studies help gain a deep insight into heterogeneous chemistry processes taking place on dust particles as a result of water-induced swelling and the ensuing changes in their optical properties [18]. While there have existed many studies on aerosol hygroscopicity using in situ and laboratory observation data, there have been relatively few studies in open atmospheric environment conditions in China whose aerosols are heavy and complex with significant impact on regional climate and environment [3,19]. The last section is a summary of the whole study
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
