Chemistry and aerosols in the marine boundary layer: 1-D modelling of the three ACE-2 Lagrangian experiments

Three Lagrangian experiments were conducted during IGAC's second aerosol ch aracterization experiment (ACE-2) in the area between Portugal, Tenerife an d Madeira in June/July 1997. During each Lagrangian experiment, a boundary layer air mass was followed for about 30 h, and the temporal evolution of i ts chemical and aerosol composition was documented by a series of vertical profiles and horizontal box pattern flown by the Meteorological Research Fl ight research aircraft Hercules C130. The wealth of observational data that has been collected during these three Lagrangian experiments is the basis for the development and testing of a one-dimensional Lagrangian boundary la yer model with coupled gas, aqueous, and aerosol phase chemistry. The focus of this paper is on current model limitations and strengths. We show that the model is able to represent the dynamical and chemical evolution of the marine boundary layer, in some cases requiring adjustments of the subsidenc e velocity and of the surface heat fluxes. Entrainment of a layer rich in o zone and carbon monoxide from a residual continental boundary layer into th e marine boundary layer as well as in-cloud oxidation of sulphur dioxide by hydrogen peroxide are simulated, and coherent results are obtained, concer ning the evolution of the small, presumably sulphate-ammonia aerosol mode. (C) 2000 Elsevier Science Ltd. All rights reserved.