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. We present the first observational dataset of vertically resolved global stratospheric BrONO2 distributions from July 2002 until April 2012 and compare them to results of the atmospheric chemical climate modelECHAM/MESSy Atmospheric Chemistry (EMAC). The retrieved distributions are based on space-borne measurements of infrared limb-emission spectra recorded by the Michelson Interferometer forPassive Atmospheric Sounding (MIPAS) on Envisat. The derived verticalprofiles of BrONO2 volume mixing ratios represent 10∘ latitudebins and 3 d means, separated into sunlit observations and observations in the dark. The estimated uncertainties are around 1–4 pptv, caused by spectral noise for single profiles as well as for further parameter andsystematic errors which may not improve by averaging. Vertical resolutionsrange from 3 to 8 km between 15 and 35 km altitude. All leading modes of spatial and temporal variability of stratosphericBrONO2 in the observations are well replicated by the modelsimulations: the large diurnal variability, the low values during polar winteras well as the maximum values at mid and high latitudes during summer. Three major differences between observations and model results are observed: (1) amodel underestimation of enhanced BrONO2 in the polar winterstratosphere above about 30 km of up to 15 pptv, (2) up to8 pptv higher modelled values than observed globally in the lowerstratosphere up to 25 km, most obvious during night, and (3) up to 5 pptv lower modelled concentrations at tropical latitudes between 27and 32 km during sunlit conditions. (1) is explained by the modelmissing enhanced NOx produced in the mesosphere and lowerthermosphere subsiding at high latitudes in winter. This is the first timethat observational evidence for enhancement of BrONO2 caused bymesospheric NOx production is reported. The other majorinconsistencies (2, 3) between EMAC model results and observations are studied by sensitivity runs with a 1D model. These tentatively hint at a model underestimation of heterogeneous loss of BrONO2 in the lower stratosphere, a simulatedproduction of BrONO2 that is too low during the day as well as strongly underestimated BrONO2 volume mixing ratios when loss via reaction withO(3P) is considered in addition to photolysis. However, consideringthe uncertainty ranges of model parameters and of measurements, an unambiguousidentification of the causes of the differences remains difficult. The observations have also been used to derive the total stratospheric brominecontent relative to years of stratospheric entry between 1997 and 2007. Withan average value of 21.2±1.4 pptv of Bry atmid latitudes where the modelled adjustment from BrONO2 to Bry is smallest, the MIPAS data agree with estimates ofBry derived from observations of BrO as well as fromMIPAS-Balloon measurements of BrONO2.

atmospheric chemistry and physics

The Michelson Interferometer for Passive Atmospheric Sounding global climatology of BrONO&lt;sub&gt;2&lt;/sub&gt; 2002–2012: a test for stratospheric bromine chemistry