Abstract
Abstract. The aim of the work presented here was to detect BrO in the marine boundary layer over the Eastern North-Atlantic by Multi AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS) of scattered sunlight. With this technique, information about the concentration and the vertical profile of trace gases in the atmosphere can be gained. BrO can be formed in the marine atmosphere by degradation of biogenic organohalogens or by oxidation of bromide in sea salt aerosol. BrO influences the chemistry in marine air in many ways, e.g. since it catalytically destroys ozone, changes the NO2/NO-ratio as well as the OH/HO2-ratio and oxidises DMS. However, the abundance and the significance of BrO in the marine atmosphere is not yet fully understood. We report on data collected during a ship cruise, which took place along the West African Coast in February 2007, within the framework of the Surface Ocean PRocesses in the ANthropocene project (SOPRAN). Tropospheric BrO could be detected during this cruise at peak mixing ratios of (10.2±3.7) ppt at an assumed layer height of 1 km on 18 February 2007. Furthermore, it was found that the mean BrO concentrations increased when cruising close to the African Coast suggesting that at least part of the BrO might have originated from there.
Highlights
The halogen compound bromine oxide (BrO) plays an important role in stratospheric chemistry as well as in the troposphere, because of its ability to destroy ozone in a catalytic reaction cycle
We report on data collected during a ship cruise, which took place along the West African Coast in February 2007, within the framework of the Surface Ocean PRocesses in the ANthropocene project (SOPRAN)
Martin troposphere, BrO was first positively identified in polar regions (e.g. Tuckermann et al, 1997), where it can lead to total ozone depletion (Barrie et al, 1988; Bottenheim et al, 1990)
Summary
The reactions, and the loss processes of BrO in the MBL are not yet completely understood, predictions of BrO concentrations have large uncertainties. Bromine atoms in the troposphere are quickly oxidised by O3 yielding BrO Dust plumes are another abiotic factor that might influence the release of halogen compounds in the marine boundary layer. A liquid-phase reaction of HOBr (see below) with BrO can lead to the so-called “bromine explosion” (Platt and Lehrer, 1996; Wennberg, 1999), which derives its name from the exponentially increasing release of reactive bromine into the gas phase This process appears to dominate in polar regions, but may play a role elsewhere. The West African Coast is an interesting site for the investigation of BrO, since the biological activity is very high in this region during this time of year with typical high chlorophyl concentrations and blooming plankton Iodine oxide was measured, the precursors of which are emitted mainly by algae
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