Entrainment of free tropospheric aerosols as a regulating mechanism for cloud condensation nuclei in the remote marine boundary layer

Abstract

A box model has been developed to study the formation of cloud condensation nuclei from DMS, in the unpolluted marine boundary layer (MBL). The model results are in reasonable agreement with summer observations of DMS, SO2, non-sea-salt (nss) SO4, CN, and CCN at Cape Grim. They show that entrainment of FT aerosols in the MBL quenches new particle formation within the MBL. A sensitivity/uncertainty analysis shows that most of the variation in the number concentration of MBL aerosols is due to the variation in parameters linked to the FT aerosol, whereas most of the variations in the MBL nss-sulphate mass is due to variations in the DMS flux. We conclude that FT-MBL exchange is likely to be an important mechanism that can explain both the observed levels of CN and CCN(active in stratiform clouds) in the MBL and their lack of short-term variability. -Author