Organic aerosols are believed to be important cloud condensation nuclei in the earth’s atmosphere. We suggest a chemical model for the composition, structure, and atmospheric processing of these organic aerosols. This model is stimulated by recent field measurements showing that organic compounds are a significant component of atmospheric aerosols. The proposed model organic aerosol is an "inverted micelle" consisting of an aqueous core that is encapsulated in an inert, hydrophobic organic monolayer. We propose a chemical mechanism by which the organic surface layer will be processed by reactions with atmospheric radicals. Surface reactions of the hydrocarbon film with atmospheric species such as OH, Cl, O3, and NO3 will transform the organic film. The net result is the transformation of an inert hydrophobic film to a reactive hydrophilic layer.