11 Aug 2021

11 Aug 2021

Review status: this preprint is currently under review for the journal ACP.

The MIPAS global climatology of BrONO2 2002–2012: a test for stratospheric bromine chemistry

Michael Höpfner1, Oliver Kirner2, Gerald Wetzel1, Björn-Martin Sinnhuber1, Florian Haenel1, Sören Johansson1, Johannes Orphal1, Roland Ruhnke1, Gabriele Stiller1, and Thomas von Clarmann1 Michael Höpfner et al.
  • 1Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Karlsruhe, Germany
  • 2Karlsruhe Institute of Technology, Steinbuch Centre for Computing, Karlsruhe, Germany

Abstract. 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 model EMAC. The retrieved distributions are based on space-borne measurements of infrared limb-emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat. The derived vertical profiles of BrONO2 volume mixing ratios represent 10° latitude bins and three-day means, separated into sunlit 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 and systematic errors which may not improve by averaging. Vertical resolutions range from 3 to 8 km between 15 and 35 km altitude.

All leading modes of spatial and temporal variability of stratospheric BrONO2 in the observations are well replicated by the model simulations: the large diurnal variability, the low values during polar winter as well as the maximum values at mid- and high latitudes during summer. Three major differences between observations and model results are observed: (1) a model underestimation of enhanced BrONO2 in the polar winter stratosphere above about 30 km of up to 15 pptv, (2) up to 8 pptv higher modelled values than observed globally in the lower stratosphere up to 25 km most obvious during night, and (3) up to 5 pptv lower modelled concentrations at tropical latitudes between 27 and 32 km during sunlit conditions. (1) is explained by the model missing enhanced NOx produced in the mesosphere and lower thermosphere subsiding at high latitudes in winter. This is the first time that observational evidence for enhancement of BrONO2 caused by mesospheric NOx production is reported. The other major inconsistencies (2,3) between EMAC model results and observations are studied by sensitivity runs with a 1d model. These tentatively hint to a model underestimation of heterogeneous loss of BrONO2 in the lower stratosphere, a too low simulated production of BrONO2 during day as well as strongly underestimated BrONO2 volume mixing ratios when loss via reaction with O(3P) is considered additionally to photolysis. However, considering the uncertainty ranges of model parameters and of measurements, an unambiguous identification of the causes for the differences remains difficult.

The observations have also been used to derive the total stratospheric bromine content relative to years of stratospheric entry between 1997 and 2007. With an average value of 21.2 ± 1.4 pptv of Bry at mid-latitudes where the modelled adjustment from BrONO2 to Bry is lowest, the MIPAS data agree with estimates of Bry derived from observations of BrO as well as from MIPAS-Balloon measurements of BrONO2.

Michael Höpfner et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-535', Anonymous Referee #2, 31 Aug 2021
  • RC2: 'Comment on acp-2021-535: Review of the manuscript “The MIPAS global climatology of BrONO2 2002–2012: a test for stratospheric bromine chemistry” by Hopfner et al., ACPD, 2021.', Rafael Pedro Fernandez, 18 Sep 2021

Michael Höpfner et al.

Michael Höpfner et al.


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Short summary
BrONO2 is an important reservoir gas for inorganic stratospheric bromine linked to the chemical cycles of stratospheric ozone depletion. Presently infrared limb-sounding is the only way to measure BrONO2 in the atmosphere. We provide global distributions of BrONO2 derived from MIPAS observations 2002–2012. Comparisons with EMAC atmospheric modelling show an overall agreement and enable us to derive an independent estimate of stratospheric bromine of 21.2 ± 1.4 pptv based on the BrONO2 measurements.