Developing accurate descriptions of the role that interfacial chemistry plays in the multiphase oxidation of organic aerosol and cloud droplet nucleation remains an outstanding challenge. Using model systems, we examine how the reactive uptake kinetics of hydroxyl radicals at the aerosol surface depends upon liquid water content and common atmospheric trace gases such NO and SO2. In these systems, the OH reaction probability is observed to be a complex and non-linear function of these environmental variables and involves the complex interplay between molecular reactivity, free radical cycling, viscosity, hygroscopic growth and decomposition. To examine the importance of interfacial chemistry on the cloud condensation properties of organic aerosols new Köhler curve experiments have been developed. For realistic mixed inorganic/organic aerosols, the droplet size at activation is much larger than what would be predicted based upon bulk solubility alone and points to the important role that interfacial organic molecules play in cloud droplet formation.