Abstract: The thermodynamic process of atmospheric aerosol particles is mainly derived from the non-ideal mixing of multiple substances, which includes liquid-liquid phase separation, hygroscopic-volatilization, and nonequilibrium mass transfer. Relevant physical and chemical parameters are the basis for understanding aerosol evolution process, analyzing evolution motivation and predicting evolution path. Thus accurate single particle measurement is the key to obtain these important parameters. In this study, single aerosol droplet capture without contact for a long time is realized by using the self-developed aerosol Raman optical tweezers system, and the hygroscopic-volatilization thermodynamic evolution process of aerosol droplets in the actual atmosphere is simulated by changing the ambient relative humidity around aerosol particles. Through measuring the cavity resonance Raman signal of the single droplet particle and combining with the appropriate physical models, we accurately measured the particle size, refractive index, diffusion coefficient, volatile flux and other important physicochemical parameters of the sodium chloride, sucrose and citric acid in the hygroscopic-volatile process. Moreover, the effects of relative humidity on hygroscopic-volatilization process for organic and inorganic aerosols, as well as the possible phase transitions such as glassy and gel transition, are investigated, which provide an important reference for understanding the hygroscopic-volatilization process of actual atmospheric aerosol.

Key words: aerosol droplet, hygroscopicity, volatility, Raman optical tweezer