Karsten Suhre

An overview of the Lagrangian experiments undertaken during the North Atlantic regional Aerosol Characterisation Experiment (ACE‐2)

One of the primary aims of the North Atlantic regional Aerosol Characterisation Experiment (ACE-2) was to quantify the physical and chemical processes affecting the evolution of the major aerosol types over the North Atlantic. The best, practical way of

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.

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

Abstract Three Lagrangian experiments were conducted during IGACs second aerosol characterization experiment (ACE-2) in the area between Portugal, Tenerife and 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 its chemical and aerosol composition was documented by a series of vertical profiles and horizontal box pattern flown by the Meteorological Research Flight 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 layer 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 subsidence velocity and of the surface heat fluxes. Entrainment of a layer rich in ozone and carbon monoxide from a residual continental boundary layer into the marine boundary layer as well as in-cloud oxidation of sulphur dioxide by hydrogen peroxide are simulated, and coherent results are obtained, concerning the evolution of the small, presumably sulphate–ammonia aerosol mode.

Adaptation of a cloud activation scheme to a spectral-chemical aerosol model

Development and preliminary tests of a cloud activation scheme adapted to a spectral-chemical aerosol model are presented. After some sensitivity studies bearing on changes in ambient relative humidity and various sulfate formation rates, the model is used to calculate cloud droplet nucleation for an ascending air parcel. Using the spectrum obtained with the aerosol model initialized with experimentally determined chemical concentrations, the critical radius thus obtained appears quite realistic. Sensitivity studies on the vertical velocity and on the aerosol mass concentrations display good agreement with previous published results.

A Numerical Study of DMS-Oxidation in the Marine Boundary Layer

During the last decade, dimethyl sulfide (DMS) has been invoked as an important source of non-anthropogenic sulfur (Andreae et al., 1983; Nguyen at al., 1983). Produced by marine phytoplankton, DMS is transferred to the marine boundary layer (MBL) where it is oxidized to sulfur dioxide (SO 2),methanesulfonic acid (MSA) and to sulfuric acid (H 2 SO 4). The relationship between DMS emission, cloud condensation nuclei (CCN) and cloud albedo is a problem of climatic interest (Charlson et al., 1987) to be treated on the mesoscale due to the fact that the processes involved in DMS-oxidation in the MBL have timescales typically of the order of some hours or less.