(682e) Size-Resolved CCN Activity, Mixing State, and Droplet Growth Kinetics of Atlanta Aerosols

The effects of aerosol composition (especially from organic species) on droplet formation is highly variable and uncertain, but can be largely constrained by size-resolved Cloud Condensation Nuclei (CCN) measurements. A fast method for obtaining size-resolved CCN measurements is Scanning Mobility CCN Analysis (SMCA; Nenes and Medina, in review). In SMCA, ambient monodisperse aerosol from a Differential Mobility Analyzer (operated in scanning voltage mode) is concurrently introduced into a Streamwise Thermal Gradient CCN Chamber (STGC, Roberts and Nenes, 2005) and a Condensation Particle Counter. Inversion of the concentration timeseries from both instruments yields the activation ratio (i.e., fraction of particles that act as CCN) as well as the activated droplet size, as a function of dry mobility diameter and supersaturation. In this study, we performed SMCA for aerosols sampled at Atlanta, GA during August and September of 2008. The daily trend of the mixing state, CCN activity, and droplet size of the size-resolved CCN are investigated and compared to chemical composition measurements. Inferences about the impact of photochemistry and mixing state on CCN activity and droplet growth kinetics are carried out. We also perform CCN closures (i.e., comparison of predicted and measured CCN) in which different compositional assumptions (e.g., size-invariant composition, organic insoluble/soluble with constant hygroscopicity) are addressed.