Abstract
Tropospheric BrO was measured by a ground-based remote-sensing spectrometer at Halley in Antarctica in spring 2007, and BrO was measured by satellite-borne remote-sensing spectrometers using similar spectral regions and similar Differential Optical Absorption Spectroscopy (DOAS) analyses. Near-surface BrO was simultaneously measured in situ at Halley by Chemical Ionisation Mass Spectrometer (CIMS), and in an earlier year near-surface BrO was measured at Halley over a long path by a ground-based DOAS spectrometer. During enhancement episodes, total amounts of tropospheric BrO from the ground-based remote-sensor were similar to those from space, but if we assume that the BrO was confined to the mixed layer they were very much larger than values measured by either near-surface technique. This large apparent discrepancy can be resolved if substantial amounts of BrO were in the free troposphere during most enhancement episodes. Amounts observed by the ground-based remote sensor at different elevation angles, and their formal inversions to vertical profiles, demonstrate that much of the BrO was indeed often in the free troposphere. This is consistent with the ~5 day lifetime of Bry and with the enhanced BrO observed during some Antarctic blizzards.
Highlights
Tropospheric BrO was measured by a ground-based remote-sensing spectrometer at Halley in Antarctica in spring 2007, and BrO was measured by satellite-borne remotesensing spectrometers using similar spectral regions and similar Differential Optical Absorption Spectroscopy (DOAS) analyses
The oxidising capacity of the polar troposphere is significantly altered by ozone depletion events (ODEs), during which oxidation is shifted towards control by halogen compounds
There have been earlier measurements and analyses leading to the conclusion of BrO in the polar free troposphere: from an aircraft flight of a remote sensor in the Arctic, McElroy et al [4] showed good evidence for a potential discrepancy similar to that of this work, and suggested that it could be resolved if BrO was present in the free troposphere; Parrella et al [5] speculated about BrO in the free troposphere from satellite remote-sensing measurements
Summary
Ozone in a cycle involving BrO, a trace gas that can be measured by a variety of techniques. We discuss new remote-sensing and in-situ near-surface measurements of BrO in Antarctica, and address a large and important apparent discrepancy between the remote and the in-situ measurements when using this assumption. The way our new ground-based remote sensing measurements change with elevation viewing angle leads us to conclude that BrO is frequently in the free troposphere in the Antarctic, which resolves the apparent discrepancy. This conclusion is reinforced by formal profile inversions of our groundbased remote sensing measurements. We build on this previous work to show conclusively that, on many days in the Antarctic spring of 2007, the potential discrepancy is large and that significant amounts of BrO must be in the free troposphere
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