INFLUENCE OF SOLUBLE SURFACTANT PROPERTIES ON THE ACTIVATION OF AEROSOL-PARTICLES CONTAINING INORGANIC SOLUTE

Atmospheric aerosol particles consisting of ammonium sulfate [(NH4)(2) SO4] or sodium chloride (NaCl) have reasonably well-defined hygroscopi c properties compared to other materials in aerosol particles, such as organic material. The effect of internally mixing organic compounds w ith these salts is not clear when considering the hygroscopic properti es of the resulting particles, including activation of particles in cl ouds. This research describes the activation of aerosol particles cons isting of sodium dodecyl sulfate (SDS) and NaCl solute. SDS is used as a surrogate for soluble atmospheric surfactants. Kohler theory is use d to model droplet activation while considering droplet properties suc h as surface tension (sigma), surface excess surfactant concentration, and critical micelle concentration (CMC). Reduction in critical super saturation (S-c) caused by the reduction in a (Kelvin effect) associat ed with the surfactant is dominated by the increase in S-c with the de creasing number of moles of solute in the droplet (Raoult effect) as s urfactant displaces NaCl solute mass. For an initially dry 0.1-mu m di ameter particle, S-c increases from 0.10 to 0.25 as NaCl solute mass c hanges from 100% (0% SDS solute) to 0% (100% SDS solute). Such depende nce of cloud droplet activation on mixed solute composition is importa nt when considering atmospheric chemistry and physics. The partitionin g of materials between aerosol particles and cloud drops are influence d by mixing the surfactant with NaCl. Also, inhibition of droplet acti vation when displacing NaCl solute with a high molecular weight solubl e surfactant could significantly influence the indirect effects aeroso ls have on climate change.