(203e) Airborne Size-Resolved Ccn Activity and Droplet Growth Kinetic Measurements In Pristine and Polluted Airmasses

The effects of aerosol composition (especially from organic species) on the cloud droplet formation process is highly variable and uncertain, but can be largely constrained by size-resolved measurements of Cloud Condensation Nucleus (CCN) activity (SRCM). A fast method for SRCM is Scanning Mobility CCN Analysis (SMCA; Nenes and Medina, in review), where the monodisperse aerosol output from a Differential Mobility Analyzer sampling ambient aerosol (and operated in scanning voltage mode) is concurrently introduced into a Streamwise Thermal Gradient CCN Chamber (STGC) and a Condensation particle counter; inversion of the concentration timeseries from both detectors yield the activation ratio (i.e., fraction of particles that act as CCN) and size of activated droplets, as a function of dry mobility diameter and supersaturation. From such measurements, Köhler Theory Analysis (e.g., Asa-Awuku et al., 2008; Moore et al., 2008; Padró et al., 2007) can be applied to infer the presence of surfactants, the average molecular weight of water-soluble organics and the impact of organics on droplet growth kinetics. In this study, we performed SMCA for aerosols sampled aboard the CIRPAS Twin Otter during the Marine Stratus/Stratocumulus Experiment II (MASE II) in Marina, CA in July 2007. We focus on two research flights, one carried out in marine air and one downwind of a large bovine source in the San Joaquin Valley, California; the differences seen in water-uptake properties, droplet growth kinetics as a function of organic content and character are presented.