(273a) Effects of Surfactants on the Hygroscopicity and CCN Activity of Aerosols

Surface tension is a critical parameter affecting water interactions of aerosol particles. Surfactant compounds are those which alter the surface tension of solutions via interactions at the gas/liquid interface. In the atmosphere, compounds that may act as surfactants are produced from both biogenic and anthropogenic sources. When these compounds are combined with existing aerosol particles, they have the potential to alter the surface tension of liquid-phase interfaces which may change a particleâ??s ability to take on water under sub-saturated or super-saturated conditions. In this work, we investigate the effects of various surfactants on both inorganic and organic aerosol particles on both hygroscopicity and CCN activity properties.

Dilute aqueous solutions were prepared using pure, single-component inorganic or organic compounds. These solutions were then mixed with various concentrations of different surfactants, atomized, and dried in diffusion dryers. The resulting aerosol stream was then measured for CCN activity using a DMT CCNC-100 instrument. In a second set of experiments, the same aerosols were passed through Nafion humidifier tubes exposing them to up to 97% relative humidity and their growth factors were measured using a TSI SMPS system. A final set of experiments exposed the aerosol streams first to the Nafion humidifier and then into the CCNC to determine if there was an effect of water vapor exposure time. Combined, these experiments investigated the effects of surfactant type, surfactant concentration, hygroscopicity changes, CCN changes, and kinetic limitations for water uptake by compounds that were already hygroscopic (such as ammonium sulfate) and organic compounds with much more limited water activity. The results of these experiments will be presented along with a comparison of experimental investigations available in the literature as well as some basic theory and modeling work on the subject.