The effects of atmospheric organics on aqueous droplet evaporation

Difunctional organic oxygenates are shown to have substantial effects on the evaporation rates of aqueous solution droplets. These compounds have been detected in both urban and rural environments, and their particulate concentrations assessed by investigators over the past twenty years [Grosjean (1977) Ozone and other Photochemical Oxidants. National Academy of Sciences, Washington, D.C.; Grosjean et al. (1978) Environm. Sci. Technol. 12, 313-317; Rogge et al. (1991) Atmos. Environ. 27A, 1309-1330]. To understand the effect of difunctional organic oxygenates on the transport of water at the air/water interface of single aqueous droplets, the evaporation rates of aqueous systems containing model organics were measured. The influence of organics of this type on the evaporation sate of water was also compared to aqueous solutions containing ammonium sulfate and sodium dodecyl sulfate. Light-scattering techniques were used to measure the droplet size as a function of time for electrodynamically levitated single microdroplets under conditions of controlled humidity and temperature. These techniques consisted of phase functions (angular scattering data) and morphological resonance spectra The evaporation rates for all the aqueous systems are compared to that of pure water and are found to be reduced by up to an order of magnitude. (C) 1997 Elsevier Science Ltd.