Bromine from short-lived source gases in the extratropical northern hemispheric upper troposphere and lower stratosphere (UTLS)

Medientyp: E-Artikel

Titel: Bromine from short-lived source gases in the extratropical northern hemispheric upper troposphere and lower stratosphere (UTLS)

Beteiligte: Keber, Timo [VerfasserIn]; Bönisch, Harald [VerfasserIn]; Graf, Phoebe [VerfasserIn]; Jöckel, Patrick [VerfasserIn]; Engel, Andreas [VerfasserIn]; Hartick, Carl [VerfasserIn]; Hauck, Marius [VerfasserIn]; Lefrancois, Fides [VerfasserIn]; Obersteiner, Florian [VerfasserIn]; Ringsdorf, Akima [VerfasserIn]; Schohl, Nils [VerfasserIn]; Schuck, Tanja [VerfasserIn]; Hossaini, Ryan [VerfasserIn]

Erschienen: EGU, 2020

Sprache: Englisch

DOI: https://doi.org/10.5194/acp-20-4105-2020

ISSN: 1680-7316; 1680-7324

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Beschreibung: We present novel measurements of five short-lived brominated source gases (CH2Br2, CHBr3, CH2ClBr, CHCl2Br and CHClBr2). These rather short-lived gases are an important source of bromine to the stratosphere, where they can lead to depletion of ozone. The measurements have been obtained using an in situ gas chromatography and mass spectrometry (GC–MS) system on board the High Altitude and Long Range Research Aircraft (HALO). The instrument is extremely sensitive due to the use of chemical ionization, allowing detection limits in the lower parts per quadrillion (ppq, 10−15) range. Data from three campaigns using HALO are presented, where the upper troposphere and lower stratosphere (UTLS) of the northern hemispheric 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 show 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 ratios 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 with emissions mainly confined to low latitudes cannot reproduce the observed latitudinal distributions and will tend to overestimate organic 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 ...

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