Abstract
Abstract. This article reports on satellite observations of iodine monoxide (IO) and bromine monoxide (BrO). The region of interest is Antarctica in the time between spring and autumn. Both molecules, IO and BrO, are reactive halogen species and strongly influence tropospheric composition. As a result, a better understanding of their spatial distribution and temporal evolution is necessary to assess accurately their role in tropospheric chemistry. Especially in the case of IO, information on its present magnitude, spatial distribution patterns and source regions is still sparse. The present study is based on six years of SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY) data recorded in nadir viewing geometry. Multi-year averages of monthly mean IO columns are presented and compared to the distributions of BrO. Influences of the IO air mass factor and the IO absorption cross section temperature dependence on the absolute vertical columns are discussed. The long-term observations of IO and BrO columns yield new insight into the temporal and spatial variation of IO above the Antarctic region. The occurrence of IO on Antarctic sea ice in late spring (November) is discovered and presented. In addition, the comparison between IO and BrO distributions show many differences, which argues for different mechanisms and individual nature of the release of the two halogen oxide precursors. The state of the ecosystem, in particular the changing condition of the sea ice in late spring, is used to explain the observations of the IO behaviour over Antarctica and the differences between IO and BrO distributions.
Highlights
Reactive halogens such as iodine, bromine and their oxides have received growing attention in the past years owing to their strong impact on tropospheric composition
Interest is motivated by observations that bromine monoxide (BrO) acts as an oxidizing agent for gaseous mercury leading to enhanced bio-availability of mercury (Schroder et al, 1998; Steffen et al, 2008), and by clear evidence that iodine monoxide (IO) may nucleate via self-reactions to larger iodine oxide molecules (Burkholder et al, 2004) forming atmospheric particles and eventually growing to cloud condensation nuclei (O’Dowd et al, 2002; McFiggans et al, 2004; O’Dowd and Hoffmann, 2005; Saunders et al, 2010)
Six full years of SCIAMACHY nadir data have been analysed for the trace gas signatures of IO above Antarctica
Summary
Reactive halogens such as iodine, bromine and their oxides have received growing attention in the past years owing to their strong impact on tropospheric composition. The halogen oxides iodine monoxide (IO) and bromine monoxide (BrO), generated from the reaction of atomic I and Br with ozone, play a central role in these processes (Barrie et al, 1988; Solomon et al, 1994; Carpenter et al, 2003; Platt and von Glasow, 2005; Simpson et al, 2007b). Further measurement campaigns have observed IO by active and passive DOAS in the marine boundary layer (MBL) at several locations of the world, e.g. at mid-latitude coasts and (sub)-tropical marine sites (Allan et al, 2000; Peters et al, 2005; Saiz-Lopez et al, 2006; Oetjen, 2009) and in Polar Regions (Wittrock et al, 2000; Frieß et al, 2001; Saiz-Lopez et al, 2007a) with typical concentrations up to a few ppt. Simultaneous IO and BrO observations are compared, and due to the importance of the sea ice cover in this area, observations of the sea ice concentrations are used to analyse specific IO occurrences
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