Partitioning of semivolatile surface-active compounds between bulk, surface and gas phase

In submicron-sized droplets, surface partitioning of a surface-active volatile species may significantly decrease its equilibrium partial pressure, thus increasing the total flux of the surfactant from gas phase to aqueous phase. Such uptake of volatile organic species into aqueous aerosols can be followed by aqueous-phase chemistry to form low-volatility secondary organic aerosol material, leading to increased aerosol mass.

In the study, we used an air parcel model that includes simplified aqueous- and gas-phase chemistry, condensation/evaporation, and a model of aqueous-phase thermodynamics that takes into account the partitioning of surfactants between the bulk and surface phases. We modeled the uptake and aqueous-phase chemical reactions of methylglyoxal, as it is a moderate surfactant that forms less volatile secondary organic material via aqueous-phase chemical reactions with the hydroxyl radical as well as hydronium and ammonium ions.