Stratospheric BrO profiles measured at different latitudes and seasons: Atmospheric observations

Stratospheric BrO profiles were measured at different latitudes and in different seasons in 1996/97 during three flights of the LPMA/DOAS balloon gondola (LPMA/Laboratoire Physique Moleculaire et Application and DOAS/Differential Optical Absorption Spectrometry). Using direct sunlight DOAS spectrometry the following BrO mixing ratios were measured; (1) 9 to 14 ppt in the height range from 20 to 30 km (at solar zenith angles, SZA < 88 degrees) during;ascent, (2) about (14+/- 2) ppt for altitudes above the balloon float altitude at 30.6 km, 30.0 km, and 39.8 km, and (3) 5 to 10 ppt in the 20-30 km region during sunset. The lower BrO concentrations during sunset than those observed prior at daytime indicate a conversion of BrO into nighttime reservoir species (BrONO2, HOBr, and BrCl). The overall agreement of our UV spectroscopic BrO profiles with recent measurements using the chemical conversion/resonance fluorescence technique is good. Our BrO profiles are also in reasonable agreement with the present stratospheric Br-y burden and chemistry. Conversily collocated ground-based and satellite column measurements, however show significantly more total atmospheric BrO (50 - 100%) than the integrated stratospheric BrO balloon profiles can account for. This indicates a global tropospheric BrO background, estimated at 1-2 ppt.