Global evaluation of CCN formation by direct emission of sea salt and growth of ultrafine sea salt

The contribution of both the sea‐salt emissions and specifically the ultrafine (dry D p < 0.1 μm) component of these emissions to global CCN was assessed with a global model of aerosol microphysics. Four sea‐salt emissions parameterizations were incorporated into the GISS II‐prime general circulation model with the size‐resolved aerosol microphysics module, TOMAS. The results of the four simulations were compared to observations of monthly average PM 10 sea‐salt mass, sea‐salt mass size distributions, and marine aerosol number distributions. The agreement of the simulations with the observations varied greatly based on the sea‐salt emissions parameterization used, but validation of the parameterizations is limited by uncertainty in the model's wind speeds. The impact of sea‐salt aerosols on CCN concentrations was assessed by looking at the percent change in CCN(0.2%) concentrations between a simulation including both sea salt and sulfate and a simulation including sulfate alone. Two of the emissions parameterizations included ultrafine sea‐salt particles, and the contribution of the ultrafine particles to CCN(0.2%) formation was assessed by sensitivity studies. Depending on the emissions estimate used, the addition of sea salt increased CCN(0.2%) over the Southern Ocean by 150% to 500%. The highest increases resulted from the simulations that included ultrafine emissions where it was found that the ultrafine sea salt can increase CCN(0.2%) concentrations over both the Southern Ocean and Antarctica by more than 50% relative to the same parameterizations with ultrafine sea salt excluded. The sensitivity of CCN(0.2%) to ultrafine sea‐salt emissions enhances the importance of reducing the uncertainty of sea‐salt emissions parameterizations and their subsequent treatment in aerosol models.