Project C04:
Seasonality, variability and trends of halogenated trace gases in the UTLS

Brief Summary

The project aims to investigate the seasonality of halogenated trace gases in the UTLS and to improve the understanding of the importance of different transport pathways. We suggest to use existing data from HALO missions and new observations from onboard the observation platform IAGOS-CARIBIC to investigate seasonality, variability, and long-term changes of halogenated gases with a focus on short-lived compounds (VSLS). These are expected to play a more important role in the halogen budget of the stratosphere as emissions of long-lived compounds decrease. Short-lived compounds impact mostly the lowermost stratosphere, depending on their local lifetime which varies with seasonal changes of temperature and solar radiation. IAGOS-CARIBIC is a scientific project for measurements of atmospheric composition in the UTLS from onboard a regular passenger aircraft, operated by the German airline Lufthansa. The project was paused in 2020 and will after a major refitting of the instrument package be resumed in 2022. We propose to perform regular collection of air samples followed by post-flight laboratory analysis for halogenated compounds. To do this, an existing air sampling unit needs to be modified during the first year of the CRC. Once the new CARIBIC instrumentation becomes operational, flights are expected to be performed regularly every 1–2 months. Laboratory analysis will be performed using an existing gas chromatograph/mass spectrometry set-up. As first observational data from CARIBIC flights become available, the project will focus on merging the new data-set with existing data from HALO missions. Past HALO projects from which halocarbon data are available had a strong focus on the Northern Atlantic, except for the SOUTHTRAC mission which was based in South America. CARIBIC data will add a wider longitudinal coverage with flights between Germany and the Americas or Asia and will extend seasonal coverage. To derive distributions of halogen VSLS and long-lived compounds, we propose to investigate different coordinate systems. All analyses will be performed using tropopause-centred vertical coordinates. One part of the project will investigate how the choice of the coordinates influences observed variabilities of trace gas mixing ratios. Based on the extended data base, we want to systematically compare the observed distributions with model fields and investigate the representation of the chemical and transport processes in the model.

Members

Publications

Schuck, T. J., J. Degen, E. Hintsa, P. Hoor, M. Jesswein, T. Keber, D. Kunkel, F. Moore, F. Obersteiner, M. Rigby, T. Wagenhäuser, L. M. Western, A. Zahn, and A. Engel (2024): The interhemispheric gradient of SF6 in the upper troposphere. Atmospheric Chemistry and Physics 24 (1), 689–705. doi: 10.5194/acp-24-689-2024.

Jesswein, M., R. P. Fernandez, L. Berná, A. Saiz-Lopez, J.-U. Grooß, R. Hossaini, E. C. Apel, R. S. Hornbrook, E. L. Atlas, D. R. Blake, S. Montzka, T. Keber, T. Schuck, T. Wagenhäuser, and A. Engel (2022): Global seasonal distribution of CH₂Br₂ and CHBr₃ in the upper troposphere and lower stratosphere. Atmospheric Chemistry and Physics 22 (22), 15049–15070. doi: https://doi.org/10.5194/acp-22-15049-2022.