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

Abstract

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. Copyright 2006 by the American Geophysical Union.