Ground-based measurements of tropospheric and stratospheric BrO at Arrival Heights, Antarctica

Ground-based measurements of BrO slant column densities (SCDs) were performed using zenith shy DOAS (Differential Optical Absorption Spectroscopy) during autumn (February to May) and spring (August to October) of 1995 at Arrival Heights (77.8 degrees S, 166.7 degrees E). In both August and September, single episodes of sudden large BrO column enhancement (of magnitude 3.5 and 3.2 x 10(14) molec. cm(-2) respectively) were observed. The episode in August did not coincide with changes of other stratospheric parameters (OClO, NO2 and temperature). Furthermore, the diurnal variation in the SCD during these events was indicative of a tropospheric rather than a stratospheric absorber. The tropospheric BrO mixing ratios deduced from the data are similar to those observed by ground-based measurements in the Arctic boundary layer (similar to 30 ppt). Simultaneous balloon soundings, one during each of the two events, showed statistically significant (2 sigma) tropospheric ozone depletion between 0.5 and 2km in August and 1.5 and 2.8 km in September. Our results strongly suggest that halogen catalysed boundary layer ozone depletion not only occurs in the Arctic but also in Antarctica. This has the implication that Arctic Haze and anthropogenic influence is unlikely as a cause for this phenomenon.