Abstract
In recent models the formation of secondary organic aerosol has been described by absorption of semivolatile oxidation products to an organic aerosol mixture and/or dissolution into an aerosol aqueous phase. In coastal areas, freshly formed sea‐salt aerosol absorbs secondary semivolatile organic oxidation products into its surface organic layer, which consequently allows for the partitioning of the secondary organics to the sea‐salt aerosol brine core. This process is modeled in the present study. Equilibrium between the gas phase and a continental primary organic aerosol phase, a sea‐salt organic layer, and a continental aqueous aerosol is maintained, as is equilibrium between the organic layer and the brine core. Within aqueous phases, dissociation of acidic species is considered, and charge balance determines pH. Six semivolatile organic oxidation products that have been observed as secondary organic aerosol constituents, eight primary organic aerosol constituents representative of urban aerosols, five sea‐salt organic layer species, and four organic components of the brine core are described molecularly. Numerical iteration techniques are used to solve the relevant nonlinear governing equations for the concentrations of each product in each aerosol phase and the gas phase, as well as for the pH of the relevant aqueous phases. Variables of interest include ambient temperature and species concentrations. Results indicate that the aqueous aerosols and the sea‐salt aerosol brine core are the most efficient media for absorption under the conditions described, that organic layers enhance the partitioning to the brine core, and that secondary organic acids contribute to the acidification of the sea‐salt aerosol brine core.