Further Cryogenic Separation and Mass Spectrometry Developments: Towards Ambient Air Methane Clumped Isotopes Measurements

Houston, A. , Gazetas, O., Defratyka, S., Arnold, T. and Clog, M. (2024) Further Cryogenic Separation and Mass Spectrometry Developments: Towards Ambient Air Methane Clumped Isotopes Measurements. EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024. (doi: 10.5194/egusphere-egu24-11447) (Accepted for Publication)

Abstract

The multiply-substituted isotopologues of methane are of significant interest due to their increased ability to distinguish between methane formation and destruction processes, in comparison to singly-substituted isotopologues, as shown previously by Thiagarajan et al.(2022) and Sivan et al.(2022). Methane isotopologues, unlike the isotopologues of carbon dioxide, do not easily transition towards thermodynamic equilibrium in the atmosphere and therefore, ambient air methane isotopologues, offer constraints on the atmospheric methane sources and sinks (Chung and Arnold, 2021). These processes potentially offer new insight into the causes of variation in methane concentrations in the last two decades. We present developments in the separation of the components of air, using a helium-cooled cryostat. Working on both pre-concentrated air mixtures and laboratory created gas mixtures, we extract methane from the contaminants and other atmospheric gases using the cryostat, applicable to a minimum methane concentration of ~1% (Stolper et al., 2015), then we analyse using a TFS Ultra HR-IRMS. We demonstrate that our cryostat separations successfully extract methane and krypton from laboratory gas mixtures containing the components of atmospheric air, without causing methane fractionation. We also present further developments in measuring and calibrating the isotopologues of methane by high-resolution mass spectrometry. We successfully created thermodynamically equilibrated samples of methane in the 250-500oC range using a nickel catalyst and are working on the 1-250oC range using a γ-Al2O3 catalyst (Eldridge et al., 2019). It is essential to have an extensive calibration curve to best constrain the effects of scale compression on the calculated deltas and therefore reduce sources of further error, hence the extension of this calibration range. Further work will add additional reference and sample points to the absolute reference frame created by the equilibrated samples, optimise the cryogenic/gas chromatographic purification methods for more complex gas mixtures, and optimise the IRMS workflow to reduce the necessary air sample sizes.

• Item Type: Conference or Workshop Item
• Additional Information: Poster presentation.
• Status: Accepted for Publication
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Clog, Dr Matthieu and Houston, Dr Andrew
• Authors: Houston, A., Gazetas, O., Defratyka, S., Arnold, T., and Clog, M.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre