Long-lived greenhouse gases in the extra-tropical tropopause region

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Mixing ratios of the most relevant long-lived greenhouse gases keep increasing in the atmosphere due to ongoing athprogenic emissions. The most dominant greenhouse gases are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). In addition to their relevance as potent gaseous climate forces, these gase exhibit strong gradients across the tropopause and are therefore suited as tracers for atmospheric transport processes. With an atmospheric lifetime of approximately 850 years and continuisly increasin mixing ratios, sulfur hexafluoride (SF6) is frequently used as a tracer of the age of air, an indicator of air mass transport in the stratosphere.The proposed project aims at the harmonization and scientific evaluation of existing measurements from the tropopause region from the IAGOS-CARIBIC observational platform of these four main greenhouse gases and long-lived halogenated trace gases with high global warming potentials. Data cover the period 2005-2020 and as part of the project will be combined with further existing data from measurements onbard the German research aircraft HALO. Data analysis will target trends of greenhouse gas mixing ratios in the upper troposphere, in particular their time lags to ground observations, the variability of long-lived greenhouse gases in the tropopause region, and the identification and source attribution of high mixing ratios encountered in the upper troposphere. The overalll aim is an improved understanding of atmospheric transport processes in and into the tropopause region.In addition, an existing laboratory set-up for detection of halogenated trace gases in air samples based on gas chromatography (GC) coupled with mass spectrometry is to be extended with a small GC unit for detection of SF6 at minimized sample volume consumption. The project plan proposes to investigate options for the non-radioactive detection of SF6 based on pulsed discharge detectors. Such detectors are generally suited for measurements of SF6 but have up to now not been used for measurement of SF6 in the atmosphere. Alternatively, the established detection with an electron capture detector (based on radioactive decay of a Nickel isotope) is foreseen.