Due to the contribution from very short lived substances the current stratospheric bromine loading is uncertain with estimates between 0 and 8 ppt. Bromine in the radical form bromine monoxide (BrO) plays a key role in stratospheric ozone depletion processes both at middle and polar latitudes. At southern midlatitudes reactions involving bromine account for 25% of total ozone loss and this increases to ~40% of the ozone loss over Antarctica. In the troposphere the BrO is present in polar explosion events, with implications for the bio-geochemical cycling of mercury. The ubiquitous presence of BrO in the free troposphere is debated to be between 0 and 2 ppt. Spectroscopic measurements of BrO using ground-based direct sun and zenith sky viewing geometries are combined in an optimal estimation retrieval algorithm to obtain tropospheric and stratospheric columns of BrO. The retrieval technique is detailed and case studies of Lauder, New Zealand and Arrival Heights, Antarctica are presented.