Modeling the chemistry of the marine boundary layer: Sulphate formation and the role of sea‐salt aerosol particles

A one‐dimensional model is presented that interactively simulates the dynamics and the gas‐aqueous phase chemistry of the cloud‐topped marine boundary layer. The model is described and tested using observations from the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) measurement campaign. The comparison generally indicates satisfactory agreement for dynamical properties and chemical species, except for SO 2 . We present several explanations for this discrepancy. However, a conclusive account is dependent on quantitative information about free tropospheric SO 2 and H 2 O 2 that is not available. Furthermore, a series of sensitivity runs is presented to explain the large quantities of non‐sea‐salt sulphate associated with sea‐salt particles, as observed during ASTEX/MAGE. The main conclusions are that most sulphate associated with sea‐salt particles is formed in cloud droplets that subsequently evaporate and that only a small amount is formed in deliquesced aerosol particles. The model results are sensitive to changes in the assumed sea‐salt emission rate and the overall aerosol size distribution. The latter indicates that a shift in the sea‐salt aerosol distribution toward the smaller particle sizes might explain the observed amount of sulphate associated with sea‐salt particles.