Abstract: Hygroscopic aerosols can take up water in ambient air, and their particle size will change with the increase of relative humidity, leading to dramatic changes in optical properties (such as extinction, scattering and absorption coefficients, and single scattering albedo, etc.). The hygroscopic growth factors of aerosol optical properties (the ratio of optical parameters in wet state to dry state) are characteristic parameters representing the growth capacities of aerosols optical hygroscopicity, and also key parameters in assessing the effects of aerosols on atmospheric visibility and radiative forcing. Thus, accurate measurment of optical hygroscopic growth factors is of great significance for the evaluation of aerosol environment and climate effects. The optical hygroscopic growth measurement system consists of an optical measurement device and a humidity control system. The humidity adjustment system is used to change and control the relative humidity of samples, and the optical measurement device measures the corresponding changes of optical parameters in real time to achieve the on-line measurement of optical hygroscopic properties. In view of the significance of aerosol hygroscopicity research, the existing optical hygroscopic measurement methods and their applications are analyzed and compared comprehensively, and the research directions of measurement techniques and experimental works on aerosol hygroscopicity in the future are prospected.

Key words: aerosols, optical properties, hygroscopic properties, measurement methods