Characterizing the hygroscopicity and volatility of single levitated aerosol droplets via optical tweezers-Raman spectroscopy

The hygroscopicity and volatility of airborne particles depict the thermodynamic process of the gas-particle partition of semivolatile organic components, which then have substantial impacts on the atmospheric chemistry and lifetime of aerosols. Characterizing relevant physical and chemical parameters is the base for understanding the aerosol evolution process, analyzing evolution motivation and predicting the evolution path. In this work, we captured single levitated aerosol droplets without any contact using a self-developed aerosol optical tweezers (AOT) system, simulated the hygroscopic-volatilization thermodynamic evolution process of ambient aerosols by changing the relative humidity around the trapped droplet, and measured key thermodynamic parameters via Raman spectroscopy including the particle size, refractive index, diffusion coefficient, volatile flux, and vapor pressure. Moreover, possible phase transitions in the aerosol droplets such as glassy and gel transitions were discussed, which provided an important reference for understanding the behaviors of actual atmospheric aerosols.