Abstract
Abstract. There are few observations of speciated inorganic bromine in polar regions against which to test current theory. Here we report the first high temporal resolution measurements of Br2, BrCl and BrO in coastal Antarctica, made at Halley during spring 2007 using a Chemical Ionisation Mass Spectrometer (CIMS). We find indications for an artefact in daytime BrCl measurements arising from conversion of HOBr, similar to that already identified for observations of Br2 made using a similar CIMS method. Using the MISTRA model, we estimate that the artefact represents a conversion of HOBr to Br2 of the order of several tens of percent, while that for HOBr to BrCl is less but non-negligible. If the artefact is indeed due to HOBr conversion, then nighttime observations were unaffected. It also appears that all daytime BrO observations were artefact-free. Mixing ratios of BrO, Br2 and BrCl ranged from instrumental detection limits to 13 pptv (daytime), 45 pptv (nighttime), and 6 pptv (nighttime), respectively. We see considerable variability in the Br2 and BrCl observations over the measurement period which is strongly linked to the prevailing meteorology, and thus air mass origin. Higher mixing ratios of these species were generally observed when air had passed over the sea-ice zone prior to arrival at Halley, than from over the continent. Variation in the diurnal structure of BrO is linked to previous model work where differences in the photolysis spectra of Br2 and O3 is suggested to lead to a BrO maximum at sunrise and sunset, rather than a noon-time maxima. This suite of Antarctic data provides the first analogue to similar measurements made in the Arctic, and of note is that our maximum measured BrCl (nighttime) is less than half of the maximum measured during a similar period (spring-time) in the Arctic (also nighttime). This difference in maximum measured BrCl may also be the cause of a difference in the Br2 : BrCl ratio between the Arctic and Antarctic. An unusual event of trans-continental air mass transport appears to have been responsible for severe surface ozone depletion observed at Halley over a 2-day period. The halogen source region appears to be the Bellingshausen Sea, to the west of the Antarctic Peninsula, with the air mass having spent 3 1/2 days in complete darkness crossing the continent prior to arrival at Halley.
Highlights
IntroductionHigher mixing ratios of these species were gen- (BL) ODEs in the Antarctic in the mid-1990s (Kreher et al, erally observed when air had passed over the sea-ice zone 1996; Wessel et al, 1998) and the coincident detection of prior to arrival at Halley, than from over the continent
Ozone mixing ratios can ments made in the Arctic, and of note is that our maximum fall from background amounts to bemeasured BrCl is less than half of the maximum low instrumental detection liSmoitslid(roEugahlrytha few parts per measured during a similar period in the Arctic billion by volume, ppbv) within a few minutes and remain suppressed for on the order of hours to days
We report the first high temporal resolution measurements of BrO, Br2 and BrCl in coastal Antarctica, made during spring 2007 using a Chemical Ionisation Mass Spectrometer (CIMS) instrument
Summary
Higher mixing ratios of these species were gen- (BL) ODEs in the Antarctic in the mid-1990s (Kreher et al, erally observed when air had passed over the sea-ice zone 1996; Wessel et al, 1998) and the coincident detection of prior to arrival at Halley, than from over the continent. Br2 and O3 is suggested to lead to a BrO maximum at sun- torical ozone data from Halley, that ozone depletion events rise and sunset, rather than a noon-time maxima. Ozone mixing ratios can ments made in the Arctic, and of note is that our maximum fall from background amounts (typically 30–40 ppbv) to bemeasured BrCl (nighttime) is less than half of the maximum low instrumental detection liSmoitslid(roEugahlrytha few parts per measured during a similar period (spring-time) in the Arctic billion by volume, ppbv) within a few minutes and remain suppressed for on the order of hours to days
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