Study on the Mass transfer and hygroscopic behavior of glucose / ammonium sulfate aerosol droplets

Abstract

Organic aerosols can form semisolid state, glassy state and high viscous state in the atmosphere, which makes aerosols show nonequilibrium kinetic characteristics following the loss of water due to the extended timescales for diffusive mixing. In this study, aerosol optical tweezers (AOTs) and confocal Raman spectroscopy are utilized to investigate the mass transfer of water and the hygroscopicity of internally mixed glucose/ammonium sulfate aerosol droplets with different organic/inorganic molar ratios (OIRs). The characteristic time ratio between the droplet radius and the RH is calculated to describe the mass transfer of water in the droplets. The results shown that the characteristic time ratio of the mixed glucose/ammonium sulfate aerosol droplets is apparently lower than that of pure glucose droplets. And the characteristic time ratio of the mixed droplets decreases with the increase of ammonium sulfate. The hygroscopicity of mixed glucose/ammonium sulfate aerosol droplets is greatly affected by high viscosity organic matter, and the glassy state of glucose suppresses the crystallization of ammonium sulfate in the system. Compared with the pure ammonium sulfate droplets, the efflorescence relative humidity (ERH) of the mixed glucose/ammonium sulfate droplets is delayed and the deliquescence relative humidity (DRH) is advanced. The ERH of the mixed aerosol droplets with molar ratios of 1:4, 1:3 and 1:2 is 35 ± 2%, 32 ± 2.5% and 30 ± 1.5% RH, respectively. And the DRH of the mixed aerosol droplets is 78 ± 1.5%, 76 ± 2% and 74 ± 2.5% RH, respectively. These results improve the understanding of the physical and chemical properties of super viscous organic/inorganic mixed aerosols, and might have important implications for atmospheric chemistry.