Spectroscopic measurements of BrO using direct sun and zenith sky viewinggeometries are combined in an optimal estimation retrieval algorithm to obtaintropospheric and stratospheric columns of BrO. Twenty-two twilight periods areinvestigated over Arrival Heights, Antarctica (77.8 S, 166.7 E) during the polar springperiod of 2002. This paper presents the first tropospheric and stratospheric BrO columnretrievals from UV-visible ground-based measurements for a polar location. A directcomparison is made between stratospheric columns retrieved at 80 , 84 , and 88 solarzenith angles (SZA) from the spectroscopic measurements and those calculated by theSLIMCAT three-dimensional chemical transport model. The ground-based column BrOobservations are consistent with a SLIMCAT stratospheric Bry loading of 21.2 parts pertrillion at 20 km. SLIMCAT reproduces the observed sunrise column BrO increase butdoes not match the sunset observations, which display less variation. The significantwarming of the Antarctic polar stratosphere in 2002 led to highly variable stratosphericcolumns being observed. The observed column BrO decreased with the transition fromvortex to extravortex air on 21 September but did not change much following the return ofthe vortex on 12 October. For the tropospheric column, an almost normal distributionconsistent with a background of 0.3 ± 0.3 1013 molecules cm 2 is observed from theground (80 , 84 , and 88 for both sunrise and sunset). A statistically significant bromineexplosion event (at the 2s level) was detected at the end of October with a troposphericcolumn of 1.8 ± 0.1 1013 molecules cm 2. The measured tropospheric columns arecompared with the tropospheric Model of Atmospheric Transport and ChemistryMaxPlanck Institute for Chemistry version model. The tropospheric BrO sunrise columnobservations can only be explained with an additional bromine source other thandecomposition of CH3Br and downward transport of long-lived bromine from thestratosphere. A comparison with the spaceborne Global Ozone Monitoring Experiment(GOME) found the total columns observed from the ground to be 1625% smaller thanthe total columns observed by GOME for SZAs between 80 and 88 .