Stratospheric BrO profiles measured at different latitudes and seasons: Instrument description, spectral analysis and profile retrieval

Measurements of stratospheric BrO profiles are reported using a novel DOAS instrument (Differential Optical Absorption Spectrometry) operated on the LPMA/DOAS balloon gondola (LPMA/Laboratoire de Physique Moléculaire et Applications) during three flights (León, Nov. 23, 1996, Kiruna, Feb. 14, 1997, and Gap, June 20, 1997). BrO was detected by its vibrational bands (4–0 at 354.7nm; 5–0 at 348.8nm) of the A(²π)←X(²π) transition in direct sunlight spectra from balloon ascent, descent and during solar occultation at maximum (float) altitude. We show that our accuracy is about ±18% (1 σ) during balloon ascent (solar zenith angles, SZA < 88°), and about ±25% for solar occultation measurements. For altitudes above the balloon float our observations indicate average BrO mixing ratios of (14.4±2.5)ppt, (15.6±2.8)ppt, and (15.3±2.8)ppt above 30.6km, 30.0km, and 39.8km, respectively.