Investigation of water adsorption and hygroscopicity of atmospherically relevant particles using a commercial vapor sorption analyzer

Abstract

Abstract. Water adsorption and hygroscopicity are among the most important physicochemical properties of aerosol particles, largely determining their impacts on atmospheric chemistry, radiative forcing, and climate. Measurements of water adsorption and hygroscopicity of nonspherical particles under subsaturated conditions are nontrivial because many widely used techniques require the assumption of particle sphericity. In this work we describe a method to directly quantify water adsorption and mass hygroscopic growth of atmospheric particles for temperature in the range of 5-30 • C, using a commercial vapor sorption analyzer. A detailed description of instrumental configuration and experimental procedures, including relative humidity (RH) calibration, is provided first. It is then demonstrated that for (NH 4 ) 2 SO 4 and NaCl, deliquescence relative humidities and mass hygroscopic growth factors measured using this method show good agreements with experimental and/or theoretical data from literature. To illustrate its ability to measure water uptake by particles with low hygroscopicity, we used this instrument to investigate water adsorption by CaSO 4 · 2H 2 O as a function of RH at 25 • C. The mass hygroscopic growth factor of CaSO 4 · 2H 2 O at 95 % RH, relative to that under dry conditions (RH < 1 %), was determined to be (0.450 ± 0.004) % (1σ ). In addition, it is shown that this instrument can reliably measure a relative mass change of 0.025 %. Overall, we have demonstrated that this commercial instrument provides a simple, sensitive, and robust method to investigate water adsorption and hygroscopicity of atmospheric particles.

Synergistic effect of water-soluble species and relative humidity on morphological changes in aerosol particles in the Beijing megacity during severe pollution episodes

“…Such kinds of mineral dust particles coated with anthropogenic pollutants have been observed by a number of previous electro-microscopic-based studies. Previous studies (Reitz et al, 2011;Gu et al, 2017;Ma et al, 2013) also demonstrated the presence of cSO 4 on the surface of dust particles; nevertheless, we think the effect of cSO 4 on the decrease in δ Dp=5 value was negligible because the mass fraction of cSO 4 was tiny (< 0.02) and the CaSO 4 was hard to dissolve in limited amounts of aerosol liquid water content. Note that the chemical compounds (such as kaolinite, illite, humic matter, etc.)…”

“…Such a characteristic is widely used to distinguish dust and spherical particles by both ground-based lidar observations (Asian Dust and Aerosol Lidar Observation Network, AD-Net; Shimizu et al, 2016) and satellite remote sensing (Cloud-Aerosol Lidar with Orthogonal Polarization, CALIOP; on board the CALIPSO satellite; Winker et al, 2009;Zhang et al, 2018) presuming that spherical particles and dust were externally mixed. On the basis of this technique, studies on spatially resolved distributions Uno et al, 2008), transport patterns ) of pollution and dust, and data processing algorithms (Nishizawa et al, 2007(Nishizawa et al, , 2011Winker et al, 2009) have been widely performed. For instance, Shimizu et al (2004) summarized the contributions of different aerosol types on the total backscattering coefficient at multiple sites in East Asia using three-channel Mie scatting lidar data.…”

A review of experimental techniques for aerosol hygroscopicity studies

“…Phys. Very recently, Tang and coworkers systematically evaluated the performance of a vapor sorption analyser to investigate hygroscopic properties of particles of atmospheric relevance (Gu et al, 2017b). The instrument, with its schematic diagram shown in Fig.…”

“…The vapor sorption analyzer was used to examine hygroscopicity of CaSO4•2H2O at 25 o C (Gu et al, 2017b), and the results are displayed in Fig. 5.…”

Reply to Ref #2

“…5b, a relative mass change of < 0.025 % within 6 h could be accurately determined. This instrument was further employed to investigate hygroscopic properties of perchlorates (Gu et al, 2017a;Jia et al, 2018), Ca-and Mg-containing salts (Guo et al, 2019), and primary biological particles , which play significant roles in the environments of the Earth and Mars. To our knowledge, the VSA technique has not yet been used to explore hygroscopic properties of ambient aerosol particles.…”