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.