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A mixed-layer model for the concentration and evolution of marine aerosols is presented. The ambient aerosol spectrum is divided into continental and sea-salt components and transformed to a reference saturation ratio. The temporal evolution of the aerosol spectrum is predicted from rate equations that require specification of the mixed-layer depth. particle production at the surface, and particle entrainment into the mixed layer from aloft. The model was tested against a marine data set obtained off Southern California during the CEWCOM-78 experiment. The test was carried out with two different methods of obtaining the relevant meteorological and aerosol parameters: (i) actual measurements and (ii) dynamic boundary layer model prediction and parameterization. In the first case. the model reproduced the aerosol data within a factor of 1.5. while in the second case, the uncertainty factor was 2.0. In either case. the model only modestly out-performs a much simpler model, which uses only local specification of the wind speed and humidity.

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The distribution of aerosols in the marine boundary layer can be viewed as a dynamic balance of production, transport and removal processes. The balance of these processes can be represented by a simple mixed -layer model.The vertical distribution of aerosols is dominated by turbulent transport. When mixing is dominated by surface shear or cloudtop cooling (as is typical in mid-latitudes), a single "well-mixed" layer is sufficient to describe the aerosol profile. When scattered cumulus clouds are present (called the "trade wind" or "weak cumulus convection" regime), the well -mixed layer is confined to the region below cloud base.In the region above cloudbase and below cloudtops, strong vertical gradients of aerosol concentration may be observed.A simple parameterization of this gradient is presented.