AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Surfactant Effect on Cloud Condensation Nuclei for Two-Component Internally Mixed Aerosols
SARAH SUDA PETTERS, Markus Petters, North Carolina State University
Abstract Number: 466 Working Group: Aerosols, Clouds, and Climate
Abstract Cloud condensation nuclei (CCN) are essential for the formation of clouds. Their abundance, size, and chemical composition of can affect the cloud’s microphysical properties and albedo. Thus the ability of aerosols to serve as CCN is central to their role in climate. The CCN activity of internally mixed particles can be predicted from the averaged CCN activity of the chemical components. However, surface active compounds alter a particle’s CCN activity by reducing droplet surface tension and partitioning to the droplet surface. Here we present experimental data on the CCN activity of particles composed of two-component mixtures of surfactants and non-surfactants. We tested eleven binary systems using strong ionic (sodium dodecyl sulfate) and non-ionic surfactants (Zonyl FS-300 and Triton X-100) and three non-surfactant compounds (glucose, ammonium sulfate, and sodium chloride), with 20–30 mixing fractions per system. We also tested for kinetic limitations to surfactant partitioning in nascent droplets by introducing a humidification and delay pre-treatment before some CCN activation measurements, allowing additional time for the surfactant to equilibrate. Our results show that kappa values for cloud droplet activation can deviate up to 100% relative to predictions made from measurements of bulk surface tension and simplified versions of Köhler theory that account for surface tension reduction and surface partitioning. The data obtained with and without humidification were indistinguishable within measurement uncertainty, suggesting that dynamic surface tension does not need to be considered in Köhler theory. We anticipate our results describing the CCN activity of mixed aerosols including surfactants may be used to improve the understanding of CCN activity for complex ambient aerosols.