Abstract. Marine boundary layer (MBL) clouds cover a large area of our planet and play a significant role in controlling Earth's albedo. Since MBL cloud droplets form on cloud condensation nuclei (CCN), it is important to understand their origin and evolution. Experimental and modeling efforts suggest that remote MBL CCN are formed on sea salt aerosols and on particles generated by gas-to-particle conversion in MBL and free troposphere. Observations show also that in the time intervals between rain or pollution events, the aerosol size distribution reaches a remarkably stable regime, with little variability of CCN concentration. The observed stability of the aerosol size distribution in remote MBL is supported by a qualitative and numerical analysis of the dynamic system describing the main processes contributing to formation and decay of aerosol particles. The model includes the time evolution of sulfuric acid, nuclei formed by homogeneous nucleation, and CCN concentrations. The major chemical and microphysical processes of MBL aerosols and entrainment from free troposphere are included. It is shown that the dynamic system thus obtained has a stable node as critical point for a large range of realistic diurnal average production rates of sulfuric acid and other key parameters. Moreover, the diurnal variations of aerosol concentration tend to a steady cycle in about 5 days after a dramatic perturbation (such as a rain event), consistent with the empirical evidence of steady CCN concentration in remote MBL.
Copyright 1998 by the American Geophysical Union.