Abstract
Tropospheric BrO profiles (about 0.6±0.2 ppt, and 2.0±0.8 ppt at profile maximum) were measured for the first time. Our measurements add new information to recent speculations—based on indirect evidence— of BrO possibly being ubiquitous in the free troposphere [Harder et al., 1998; Frieß et al., 1999; Van Roozendael et al., 1999; Pundt et al., 2000]. Our study relies on a detailed comparison of BrO slant column densities (BrO‐SCD) measured in the troposphere from the LPMA/DOAS (Laboratoire de Physique Moléculaire et Applications and Differential Optical Absorption Spectroscopy) gondola by direct Sun absorption, and BrO‐SCD values subsequently measured in the lowermost stratosphere during balloon ascent. The difference in total atmospheric BrO‐SCDs measured in the troposphere and lowermost stratosphere—after a suitable correction for the change in BrO due to photochemistry and the observation geometry—is then attributed to tropospheric BrO.
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