Evaporation kinetics of aqueous acetic acid droplets: effects of soluble organic aerosol components on the mechanism of water evaporation

The presence of organic surfactants in atmospheric aerosol may lead to a depression of cloud droplet growth and evaporation rates affecting the radiative properties and lifetime of clouds. Both the magnitude and mechanism of this effect, however, remain poorly constrained. We have used Raman thermometry measurements of freely evaporating micro-droplets to determine evaporation coefficients for several concentrations of acetic acid, which is ubiquitous in atmospheric aerosol and has been shown to adsorb strongly to the air-water interface. We find no suppression of the evaporation kinetics over the concentration range studied (1-5 M). The evaporation coefficient determined for 2 M acetic acid is 0.53 +/- 0.12, indistinguishable from that of pure water (0.62 +/- 0.09).