[1] The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) onboard the ENVISAT satellite provides for the first time a global view on stratospheric bromine monoxide (BrO). Here we focus on a 10 day period in September 2002. The BrO retrievals are compared with modeled BrO profiles, based on estimated inorganic bromine (Br y ) from CFC-11 retrievals by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on ENVISAT and the calculated BrO/ Br y ratio from a photochemical model constrained by SCIAMACHY NO 2 retrievals. The BrO observations are broadly consistent with our current understanding of stratospheric bromine chemistry and a total stratospheric bromine loading of 18 ± 3 pptv. Comparisons between the measured stratospheric BrO column and the simultaneously measured total BrO column from SCIAMACHY nadir observations suggest an average global background tropospheric BrO mixing ratio of 1.0 ± 0.5 pptv.

Abstract. Bromine compounds play an important role in the depletion of stratospheric ozone. We have calculated the changes in stratospheric ozone in response to changes in the halogen loading over the past decades, using a twodimensional (latitude/height) model constrained by source gas mixing ratios at the surface. Model calculations of the decrease of total column ozone since 1980 agree reasonably well with observed ozone trends, in particular when the contribution from very short-lived bromine compounds is included. Model calculations with bromine source gas mixing ratios fixed at 1959 levels, corresponding approximately to a situation with no anthropogenic bromine emissions, show an ozone column reduction between 1980 and 2005 at Northern Hemisphere mid-latitudes of only ≈55% compared to a model run including all halogen source gases. In this sense anthropogenic bromine emissions are responsible for ≈45% of the model estimated column ozone loss at Northern Hemisphere mid-latitudes. However, since a large fraction of the bromine induced ozone loss is due to the combined BrO/ClO catalytic cycle, the effect of bromine would have been smaller in the absence of anthropogenic chlorine emissions. The chemical efficiency of bromine relative to chlorine for global total ozone depletion from our model calculations, expressed by the so called α-factor, is 64 on an annual average. This value is much higher than previously published results. Updates in reaction rate constants can explain only part of the differences in α. The inclusion of bromine from very short-lived source gases has only a minor effect on the global mean α-factor.

Abstract. The contribution of bromoform to the stratospheric bromine loading is estimated using the onedimensional tropical mean model of Folkins and Martin (2005), which is constrained by observed mean profiles of temperature and humidity. In order to reach the stratosphere, bromoform needs to be lifted by deep convection into the tropical tropopause layer (TTL), above the level of zero radiative heating. The contribution of bromoform to stratospheric bromine then depends critically on the rate of removal of the degradation products of bromoform (collectively called Br y here) from the TTL, which is believed to be due to scavenging by falling ice. This relates the transport of short-lived bromine species into the stratosphere to processes of dehydration in the TTL. In the extreme case of dehydration occurring only through overshooting deep convection, the loss of Br y from the TTL may be negligible and consequently bromoform will fully contribute with its boundary layer mixing ratio to the stratospheric bromine loading, i.e. with 3 pptv for an assumed 1 pptv of bromoform in the boundary layer. For the other extreme that Br y is removed from the TTL almost instantaneously, the model calculations predict a contribution of about 0.5 pptv for the assumed 1 pptv of boundary layer bromoform. While this gives some constraints on the contribution of bromoform to stratospheric bromine, a key uncertainty in estimating the contribution of short-lived bromine source gases to the stratospheric bromine loading is the mechanism and rate of removal of Br y within the TTL.

[1] Denitrification has been studied using measurements of stratospheric HNO 3 and N 2 O by the Airborne Submillimeter Radiometer (ASUR), operated on board the NASA DC-8 during SOLVE/THESEO 2000. Lidar measurements taken on board the same aircraft have been used to distinguish between temporary uptake of HNO 3 in polar stratospheric clouds (PSCs) and denitrification events. To derive an NO y budget, ClNO 3 data by balloonborne and ground-based Fourier transform infrared measurements and a model estimate of NO x + 2N 2 O 5 have been considered. The HNO 3 profiles of sporadic ASUR measurements without PSC coverage in January suggest that denitrification had started in the vortex core region by then. Vortexwide denitrification was found in midMarch 2000. Corrected for diabatic descent using the N 2 O measurements, a vortexaveraged NO y deficit between 1.2 ± 0.9 ppb at about 16 km altitude and 5.3 ± 2.7 ppb at about 20.5 km altitude was derived compared to December 1999, based on an observed decrease in HNO 3 between 2.2 and 3.5 ppb during this time period. A shift in the NO y partitioning from HNO 3 toward ClNO 3 of about 0.4 to 0.7 ppb was observed in midMarch compared to December, indicating that chlorine deactivation was occurring. Comparisons with the SLIMCAT three-dimensional chemical transport model applying denitrification schemes based on ice and nitric acid trihydrate particles in equilibrium, respectively, reveal agreement within the error bars at higher altitudes ($19 km) but show discrepancies at lower altitudes ($16 km). It is suggested that more sophisticated denitrification schemes are needed to generally describe denitrification processes.

Abstract. The transport of very short-lived substances into the tropical upper troposphere and lower stratosphere is investigated by a three-dimensional chemical transport model using archived convective updraft mass fluxes (or detrainment rates) from the European Centre for Medium-Range Weather Forecast's ERA-Interim reanalysis. Large-scale vertical velocities are calculated from diabatic heating rates. With this approach we explicitly model the large scale subsidence in the tropical troposphere with convection taking place in fast and isolated updraft events. The model calculations agree generally well with observations of bromoform and methyl iodide from aircraft campaigns and with ozone and water vapor from sonde and satellite observations. Using a simplified treatment of dehydration and bromine product gas washout we give a range of 1.6 to 3 ppt for the contribution of bromoform to stratospheric bromine, assuming a uniform source in the boundary layer of 1 ppt. We show that the most effective region for VSLS transport into the stratosphere is the West Pacific, accounting for about 55% of the bromine from bromoform transported into the stratosphere under the supposition of a uniformly distributed source.