Arctic bromine chemistry

Evidence for the contribution of the CIO + BrO interaction is found in the detection and measurement of OCIO that is formed as a major product of this reaction, reaction (31a). This species has a very characteristic banded absorption structure in the UV and visible regions, which makes it an ideal candidate for measurement using differential optical absorption spectrometry (see Chapter 11). With this technique, enhanced levels of OCIO have been measured in both the Antarctic and the Arctic (e.g., Solomon et al., 1987, 1988 Wahner and Schiller, 1992 Sanders et al., 1993). From such measurements, it was estimated that about 20-30% of the total ozone loss observed at McMurdo during September 1987 and 1991 was due to the CIO + BrO cycle, with the remainder primarily due to the formation and photolysis of the CIO dimer (Sanders et al., 1993). The formation of OCIO from the CIO + BrO reaction has also been observed outside the polar vortex and attributed to enhanced contributions from bromine chemistry due to the heterogeneous activation of BrONOz on aerosol particles (e.g., Erie et al., 1998). 

Abbatt, J.P.D., and Nowak, J.B. (1997) Heteogeneous interactions of HBr and HOC1 with cold sulfuric add solutions implications for Arctic boundary layer bromine chemistry, J. Phys. Chem. A 101, 2131-2137. 

Significant atmospheric ozone depletion is not restricted just to the Antarctic stratosphere. In addition to other locations in the atmosphere [1], there is significant ozone depletion in the springtime Arctic tropospheric boundary layer, where bromine is much more abimdant than elsewhere, and where heterogeneous bromine chemistry is implicated in extremely rapid ozone depletion near ground level [25-27]. 

However, with the recent recognition of the potential importance of atomic chlorine and bromine under certain conditions in the Arctic at polar sunrise (e.g., see Barrie et al., 1988 and Niki and Becker, 1993), the potential for BrO and CIO chemistry has been reconsidered. As described in Chapter 6 J.4, at polar sunrise there is a rapid loss of ground-level 03 that appears to be associated with reaction with atomic bromine and at the same time, there is evidence that chlorine atoms are playing a major role in the organic removal (Jobson et al., 1994). This is consistent with reactions of sea salt particles generating atomic bromine and chlorine, although the exact nature of the reactions and halogen atom precursors remains unknown. 

The potentially strong involvement of halogens in tropospheric chemistry was first observed in the Arctic, where strong ozone depletion events were found to coincide with high levels of bromine (Barrie et al., 1988). 

Martinez M., Arnold T., and Perner D. (1999) The role of bromine and chlorine chemistry for arctic ozone depletion events in Ny-Alesund and comparison with model calculations. Ann. Geophys. 17, 941-956. 

Hausmann, M., Platt, U. Spectroscopic measurement of bromine oxide and ozone in the high Arctic during Polar Sunrise Experiment 1992. J. Geophys. Res. 99, 25399-25413 (1994) Haynes, W.M. (ed.) CRC Handbook of Chemistry and Physics, 93th ed. CRC Press, Boca Raton... 

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