Balloon-borne stratospheric BrO measurements: comparison with Envisat/SCIAMACHY BrO limb profiles

Abstract

Abstract. For the first time, results of all four existing stratospheric BrO profiling instruments, are presented and compared with reference to the SLIMCAT 3-dimensional chemical transport model (3-D CTM). Model calculations are used to infer a BrO profile validation set, measured by 3 different balloon sensors, for the new Envisat/SCIAMACHY (ENVIronment SATellite/SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) satellite instrument. The balloon observations include (a) balloon-borne in situ resonance fluorescence detection of BrO, (b) balloon-borne solar occultation DOAS measurements (Differential Optical Absorption Spectroscopy) of BrO in the UV, and (c) BrO profiling from the solar occultation SAOZ (Systeme d'Analyse par Observation Zenithale) balloon instrument. Since stratospheric BrO is subject to considerable diurnal variation and none of the measurements are performed close enough in time and space for a direct comparison, all balloon observations are considered with reference to outputs from the 3-D CTM. The referencing is performed by forward and backward air mass trajectory calculations to match the balloon with the satellite observations. The diurnal variation of BrO is considered by 1-D photochemical model calculation along the trajectories. The 1-D photochemical model is initialised with output data of the 3-D model with additional constraints on the vertical transport, the total amount and photochemistry of stratospheric bromine as given by the various balloon observations. Total [Bry]=(20.1±2.8)pptv obtained from DOAS BrO observations at mid-latitudes in 2003, serves as an upper limit of the comparison. Most of the balloon observations agree with the photochemical model predictions within their given error estimates. First retrieval exercises of BrO limb profiling from the SCIAMACHY satellite instrument agree to <±50% with the photochemically-corrected balloon observations, and tend to show less agreement below 20 km.

Retrieval of stratospheric and tropospheric BrO columns from multi-axis DOAS measurements at Reunion Island (21° S, 56° E)

“…8 for contributions of 6 pptv (cyan dashed line) and 8 pptv (blue dashed line) from the decomposition of the short-lived bromine species. The value of 8 pptv can be considered as a plausible upper limit for the contribution of the bromine short-lived species, in agreement with recent studies Salawitch et al, 2005;Schofield et al, 2006;Dorf et al, 2006a, b;Sioris et al, 2006). This also confirms the findings of Feng et al (2007), who have tested different methods of implementing the bromine source gases in the SLIMCAT model and found that the agreement between model and balloon data is significantly improved when having explicitly the short-lived source gases.…”

“…Based on a budget of the long-lived natural (CH 3 Br) and anthropogenic (CH 3 Br, CBrClF 2 , CBrF 3 , CBrF 2 CBrF 2 , CBr 2 F 2 ) organic bromine source gases observed over the last decade (Wamsley et al, 1998), the stratospheric Br y loading is currently estimated to be about 16-17 pptv. However, several recent studies Salawitch et al, 2005;Sioris et al, 2006;Sinnhuber et al, 2002Sinnhuber et al, , 2005Schofield et al, 2004a;Dorf et al, 2006a, b) have suggested that an additional contribution of about 5.6±2 pptv must be considered, due to bromine release from short-lived biogenic organic compounds (such as CHBr 3 , CH 2 Br 2 , CH 2 BrCl, CHBr 2 Cl, CHBrCl 2 , CH 2 BrCH 2 Br) or even the direct intrusion of inorganic bromine from tropospheric origin into the lower stratosphere. Inorganic bromine compounds may be produced and sustained in the free troposphere due to the decomposition of short-lived organic bromine compounds under the action of heterogeneous and/or gas-phase photochemical reactions.…”

“…BrO is also the only compound within the Br y family to be measured routinely (e.g. Wagner et al, 1998;Richter et al, 1998;Van Roozendael et al, 1999;Hausmann et al, 1994;Schofield et al, 2004a;Dorf et al, 2006a, 2005. The sources of inorganic bromine in the stratosphere originate from naturally and anthropogenically emitted bromine-containing organic gases.…”

Retrieval of stratospheric and tropospheric BrO profiles and columns using ground-based zenith-sky DOAS observations at Harestua, 60° N

“…The BrO fitting window is fixed to 332-370 nm. More details on the instrument and the retrieval algorithm can be found in Pundt et al (2002) and Dorf et al (2006b). As for the SAOZ balloon, the LPMA/DOAS balloon uses the solar occultation technique.…”

“…The BrO DOAS evaluation is performed in the 346-360 nm wavelength range and vertical profiles are retrieved using the OEM. A detailed description of the LPMA/DOAS BrO measurements can be found in Harder et al (1998 and and Dorf et al (2006b). Due to the variation of the SZA during the ascent of the balloon, a photochemical correction, calculated by using the photochemical model PSCBOX, is applied to the groundbased profiles in order to take into account this photochemical effect.…”