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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 27 Sep 2019

Submitted as: research article | 27 Sep 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Bromine from short–lived source gases in the Northern Hemisphere UTLS

Timo Keber1, Harald Bönisch1,a, Carl Hartick1,b, Marius Hauck1, Fides Lefrancois1, Florian Obersteiner1,a, Akima Ringsdorf1,c, Nils Schohl1, Tanja Schuck1, Ryan Hossaini2, Phoebe Graf3, Patrick Jöckel3, and Andreas Engel1 Timo Keber et al.
  • 1University of Frankfurt, Institute for Atmospheric and Environmental Sciences, Altenhöferallee 1, 60438 Frankfurt, Germany
  • 2Lancaster Environment Centre, Lancaster University, Lancaster, UK
  • 3Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany
  • anow at: Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
  • bnow at: Research Centre Jülich, Institute for Agrosphere (IBG-3), Wilhelm-Johnen-Straße, 52428 Jülich, Germany
  • cnow at: Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany

Abstract. We present novel measurements of five short-lived brominated source gases (CH2Br2, CHBr3, CH2ClBr, CHCl2Br and CHClBr2) obtained using a gas chromatograph-mass spectrometer system on board the High Altitude and Long Range Research Aircraft (HALO). The instrument is extremely sensitive due to the use of chemical ionisation, allowing detection limits in the lower parts per quadrillion (10−15) range. Data from three campaigns using the HALO aircraft are presented, where the Upper Troposphere/Lower Stratosphere (UTLS) of the Northern Hemisphere mid to high latitudes were sampled during winter and during late summer to early fall. We show that an observed decrease with altitude in the stratosphere is consistent with the relative lifetimes of the different compounds. Distributions of the five source gases and total organic bromine just below the tropopause shows an increase in mixing ratio with latitude, in particular during polar winter. This increase in mixing ratio is explained by increasing lifetimes at higher latitudes during winter. As the mixing ratio at the extratropical tropopause are generally higher than those derived for the tropical tropopause, extratropical troposphere-to-stratosphere transport will result in elevated levels of organic bromine in comparison to air transported over the tropical tropopause. The observations are compared to model estimates using different emission scenarios. A scenario which has emissions most strongly concentrated to low latitudes cannot reproduce the observed latitudinal distributions and will tend to overestimate bromine input through the tropical tropopause from CH2Br2 and CHBr3. Consequently, the scenario also overestimates the amount of brominated organic gases in the stratosphere. The two scenarios with the highest overall emissions of CH2Br2 tend to overestimate mixing ratios at the tropical tropopause but are in much better agreement with extratropical tropopause values, showing that not only total emissions but also latitudinal distributions in the emissions are of importance. While an increase in tropopause values with latitude is reproduced with all emission scenarios during winter, the simulated extratropical tropopause values are on average lower than the observations during late summer to fall. We show that a good knowledge of the latitudinal distribution of tropopause mixing ratios and of the fractional contributions of tropical and extratropical air is needed to derive stratospheric inorganic bromine in the lowermost stratosphere from observations. Depending on the underlying emission scenario, differences of a factor 2 in reactive bromine derived from observations and model outputs are found for the lowermost stratosphere, based on source gas injection. We conclude that a good representation of the contributions of different source regions is required in models for a robust assessment of the role of short-lived halogen source gases on ozone depletion in the UTLS.

Timo Keber et al.
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Publications Copernicus
Short summary
In this paper we summarize observations of short-lived halocarbons in the tropopause region. We show that especially during winter, the levels of short-lived bromine gases at the extratropical tropopause are higher than at the tropical tropopause. We discuss the impact of the distributions on stratospheric bromine levels and compare our observations to two models with four different emission scenarios.
In this paper we summarize observations of short-lived halocarbons in the tropopause region. We...