Atmospheric test of the J(BrONO2)/kBrO+NO2 ratio: implications for total stratospheric Bry and bromine-mediated ozone loss

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Kreycy, S., Camy-Peyret, C., Chipperfield, M. P., Dorf, M., Feng, W., Hossaini, R., Kritten, L., Werner, B., Pfeilsticker, K.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Kiruna
• Online Access: https://doi.org/10.5194/acp-13-6263-2013; https://www.atmos-chem-phys.net/13/6263/2013/

We report on time-dependent O 3 , NO 2 and BrO profiles measured by limb observations of scattered skylight in the stratosphere over Kiruna (67.9° N, 22.1° E) on 7 and 8 September 2009 during the autumn circulation turn-over. The observations are complemented by simultaneous direct solar occultation measurements around sunset and sunrise performed aboard the same stratospheric balloon payload. Supporting radiative transfer and photochemical modelling indicate that the measurements can be used to constrain the ratio J(BrONO 2 )/ k BrO+NO 2 , for which at T = 220 ± 5 K an overall 1.7 (+0.4 −0.2) larger ratio is found than recommended by the most recent Jet Propulsion Laboratory (JPL) compilation (Sander et al., 2011). Sensitivity studies reveal the major reasons are likely to be (1) a larger BrONO 2 absorption cross-section σ BrONO 2 , primarily for wavelengths larger than 300 nm, and (2) a smaller k BrO+NO 2 at 220 K than given by Sander et al. (2011). Other factors, e.g. the actinic flux and quantum yield for the dissociation of BrONO 2 , can be ruled out. The observations also have consequences for total inorganic stratospheric bromine (Br y ) estimated from stratospheric BrO measurements at high NO x loadings, since the ratio J(BrONO 2 )/ k BrO+NO 2 largely determines the stratospheric BrO/Br y ratio during daylight. Using the revised J(BrONO 2 )/ k BrO+NO 2 ratio, total stratospheric Br y is likely to be 1.4 ppt smaller than previously estimated from BrO profile measurements at high NO x loadings. This would bring estimates of Br y inferred from organic source gas measurements (e.g. CH 3 Br, the halons, CH 2 Br 2 , CHBr 3 , etc.) into closer agreement with estimates based on BrO observations (inorganic method). The consequences for stratospheric ozone due to the revised J(BrONO 2 )/ k BrO+NO 2 ratio are small (maximum −0.8%), since at high NO x (for which most Br y assessments are made) the enhanced ozone loss by overestimating Br y is compensated for by the suppressed ozone loss due to the underestimation of BrO/Br y with a smaller J(BrONO 2 )/ k BrO+NO 2 ratio.