BIOGENIC SULFUR EMISSIONS AND AEROSOLS OVER THE TROPICAL SOUTH-ATLANTIC .2. ONE-DIMENSIONAL SIMULATION OF SULFUR CHEMISTRY IN THE MARINE BOUNDARY-LAYER

Based on experimental data collected during cruise 15/3 of R/V Meteor in the tropical South Atlantic (19 degrees S), the marine sulfur cycle has been simulated with a one-dimensional coupled meteorological-chem ical model. The potential of sea-spray aerosols to act as a sink for S O2 produced from dimethylsulfide (DMS) oxidation has been examined by using a simple humidity and height dependent parameterization for sea salt aerosol distribution. Simulations show significant reduction of t otal SO2 concentrations to 27-82% of the values found in the absence o f this heterogenous process. The sulfur species concentrations calcula ted using a zero-dimensional box model agree with excess sulfate measu rements in aerosol samples. The DMS, SO2, K2SO4 (sulfates formed by SO 2 oxidation in the gas phase), and XSO(4) (sulfates formed by SO2 oxid ation in sea-spray aerosols) vertical profiles, their diurnal cycles, and turbulent fluxes have been calculated with a one-dimensional model , based solely on shipboard chemical measurements and meteorological r adiosonde soundings. Sensitivity analysis of the sea salt aerosol para meterization shows strong dependence on the assumed aerosol distributi on, thus calling for a more comprehensive approach using a coupled aer osol-meteorological model.