Airborne Observations of Halogenated Trace Gases in the Upper Troposphere and Lowermost Stratosphere
Final Report Abstract
The project investigated (i) interhemispheric gradients of halogenated compounds in the upper troposphere, (ii) airmasses influenced by the South Asian summer monsoon, and (iii) the occurrence of H(C)FOs in the tropopause region. In total, 577 samples collected in the tropopause region during flights of the IAGOS-CARIBIC container laboratory were analyzed for halocarbon mixing ratios. Deviations from the workplan were due to the fact that operation of the container lab ended in March 2020 owing to the Covid-19 pandemic. Flights are to be resumed with a newly designed container in 2023. Construction of the new air sampler as part of the reported project was delayed because new technical specifications were unclear. The sampler is now awaiting certification within the new instrument package. Additional preparational work for a new sampling control and pump unit to enable future operation of the sampler was performed, which was not part of the initial workplan. The pause in regular flights limited the scientific work within the project. In particular, fewer samples than initially projected were analyzed, and no data from the South Asian monsoon region could be obtained. A major part of the project was the investigation of interhemispheric gradients of trace gases in the upper troposphere. SF6 and N2O data from 7380 IAGOS-CARIBIC samples and halocarbon data from 577 samples were used, complemented by SF6 data from the South- TRAC mission of the HALO research aircraft. Comparing with data from observation sites, a time-lag was calculated. Results vary among substances depending on the spatial distribution of emissions and sinks, atmospheric mixing ratio trends and on tracer lifetimes. Using SF6, an average time lag with regard to the northern hemisperic mean at background observation sites of about 0.5 years was found in the tropical upper troposphere which increased to 0.7 years in the southern hemisphere. Data were compared to results from the AGAGE 12-box model.Sensitivity runs indicated that emissions derived from measurements at ground stations need to be increased by approx. 2.5 %. This indicates that adding data from the upper troposphere has the potential to improve the results of such emission estimates. In addition, the sensitivity studies showed that the default transport parametrization of the model might be too slow for transport from the northern hemisphere extra-tropics into the tropics and across the equator, but too fast regarding transport between the southern hemisphere tropics and extra-tropics. As no flights to South Asia were conducted during the project period, it was not possible to assess halocarbons in the South Asian monsoon region. Based on greenhouse gas measurements, an outlier detection algorithm was adopted that is suited to identify flask samples with tracer mixing ratios that deviate from the background timeseries. Knowing the characteristics of air masses influenced by the South Asian summer monsoon, namely elevated CH4, N2O, CO, and SF6 mixing ratios but depleted CO2, monsoon-air samples can be separated from the dataset. Finally, mixing ratios of HFO-1234yf , HFO-1234ze(E), and HCFO-1233zd(E) in the upper troposphere were investigated. These are short-livedH(C)FO which are used as replacements for longer-lived H(C)FC to reduce greenhouse gas emissions. In a small subset of 23 and 25 out of 446 samples analyzed for these compounds, HFO-1234ze(E) or HCFO-1233zd(E) was found. This indicates the potential of these substances to reach the upper troposphere. Their lifetimes are going to become longer here due to low abundances of OH and low temperatures, thus their ability to reach the upper troposphere influences their environmental impact, in particular since their atmospheric mixing ratios are rising, and there may be concern about some of their degradation products. The air sampler which was constructed within the reported project will be regularly deployed onboard the IAGOS-CARIBIC aircraft from 2023 onwards. Further studies based on the existing date are planned, namely a further analysis of interhemispheric gradients of long-lived tracers, and the further development of the outlier detection algorithm towards a more sophisticated classification scheme.
Publications
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Stability of Halocarbons in UTLS Whole Air Samples in Stainless Steel Canisters PICO presentation at the European Geosciences Union General Assembly, April 2019
Tanja Schuck, Elisa Rittmeier, Ann-Katrin Blank & Andreas Engel
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Stability of halocarbons in air samples stored in stainless- steel canisters. Atmospheric Measurement Techniques, 13(1), 73-84.
Schuck, Tanja J.; Blank, Ann-Katrin; Rittmeier, Elisa; Williams, Jonathan; Brenninkmeijer, Carl A. M.; Engel, Andreas & Zahn, Andreas
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15 years of sample collection in the Upper Troposphere with the IAGOS- CARIBIC observatory: 2005 - 2020 Inaugural lecture delivered at the Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, January 2021
Tanja Schuck
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Atmosphärenforschung uber den Wolken: 15 Jahre IAGOS-CARIBIC Invited presentation at the German Weather Service and the University Duisburg-Essen, Essener Klimagesprüche, March 2021
Tanja Schuck
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Detection of Fourth Generation Synthetic Halocarbons in the Upper Troposphere. Copernicus GmbH.
Schuck, Tanja; Meixner, Katharina; van Velthoven, Peter; O.’Doherty, Simon; Vollmer, Martin; Engel, Andreas & Zahn, Andreas
