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°S), the marine sulfur cycle has been simulated with a one-dimensional coupled meteorological-chemical model. The potential of sea-spray aerosols to act as a sink for SO₂ 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 total SO₂ concentrations to 27-82% of the values found in the absence of this heterogenous process. The sulfur species concentrations calculated using a zero-dimensional box model agree with excess sulfate measurements in aerosol samples. The DMS, SO₂, H₂SO₄ (sulfates formed by SO₂ oxidation in the gas phase), and XSO₄ (sulfates formed by SO₂ oxidation 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 radiosonde soundings. Sensitivity analysis of the sea salt aerosol parameterization shows strong dependence on the assumed aerosol distribution, thus calling for a more comprehensive approach using a coupled aerosol-meteorological model.