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 pa rticulate concentrations assessed by investigators over the past twent y years [Grosjean (1977) Ozone and other Photochemical Oxidants. Natio nal Academy of Sciences, Washington, D.C.; Grosjean et al. (1978) Envi ronm. Sci. Technol. 12, 313-317; Rogge et al. (1991) Atmos. Environ. 2 7A, 1309-1330]. To understand the effect of difunctional organic oxyge nates on the transport of water at the air/water interface of single a queous droplets, the evaporation rates of aqueous systems containing m odel 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-scatteri ng techniques were used to measure the droplet size as a function of t ime for electrodynamically levitated single microdroplets under condit ions of controlled humidity and temperature. These techniques consiste d of phase functions (angular scattering data) and morphological reson ance spectra The evaporation rates for all the aqueous systems are com pared to that of pure water and are found to be reduced by up to an or der of magnitude. (C) 1997 Elsevier Science Ltd.