Preprints
https://doi.org/10.5194/egusphere-2023-1490
https://doi.org/10.5194/egusphere-2023-1490
15 Aug 2023
 | 15 Aug 2023

Statistical evaluation of methane isotopic signatures determined during near-source measurements

Sara M. Defratyka, James L. France, Rebecca E. Fisher, Dave Lowry, Julianne M. Fernandez, Semra Bakkaloglu, Camille Yver-Kwok, Jean-Daniel Paris, Philippe Bousquet, Tim Arnold, Chris Rennick, Jon Helmore, Nigel Yarrow, and Euan G. Nisbet

Abstract. Stable carbon isotopic signatures of methane emissions are broadly used for methane source identification, apportionment, and global-scale modelling of methane sources and sinks. Thus, accurate and precise isotopic measurements of methane are crucial for methane studies from the local to global scale. To answer the need for robust and verified measurement methods, we aim at defining the best practice to determine isotopic signatures of methane sources, considering accessibility, practicality, costs, accuracy, and precision. Using Keeling and Miller-Tans methods, we verify the impact of linear fitting methods, averaging approaches, and, for Miller-Tans method, differently defined backgrounds. Verification is carried out for measurement sets using Isotope Ratio Mass Spectrometry and Cavity Ring Down Spectroscopy (CRDS). The use of AirCore for sampling, with subsequent measurements by CRDS, is also examined. Different analytical strategies introduce bias in determining isotopic signatures of methane sources, and the crucial role of rejection criteria is demonstrated. Overall, the most robust results are obtained for non-averaged data using fitting methods, which include uncertainties on x- and y-axis values.

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Sara M. Defratyka, James L. France, Rebecca E. Fisher, Dave Lowry, Julianne M. Fernandez, Semra Bakkaloglu, Camille Yver-Kwok, Jean-Daniel Paris, Philippe Bousquet, Tim Arnold, Chris Rennick, Jon Helmore, Nigel Yarrow, and Euan G. Nisbet

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1490', Anonymous Referee #1, 04 Sep 2023
    • AC2: 'Reply on RC1', Sara Defratyka, 18 Mar 2024
    • AC3: 'Reply on RC1', Sara Defratyka, 18 Mar 2024
    • AC4: 'Reply on RC1', Sara Defratyka, 18 Mar 2024
    • AC5: 'Reply on RC1', Sara Defratyka, 18 Mar 2024
  • RC2: 'Comment on egusphere-2023-1490', Anonymous Referee #2, 13 Jan 2024
    • AC1: 'Reply on RC2', Sara Defratyka, 18 Mar 2024
Sara M. Defratyka, James L. France, Rebecca E. Fisher, Dave Lowry, Julianne M. Fernandez, Semra Bakkaloglu, Camille Yver-Kwok, Jean-Daniel Paris, Philippe Bousquet, Tim Arnold, Chris Rennick, Jon Helmore, Nigel Yarrow, and Euan G. Nisbet

Data sets

Dataset: Statistical evaluation of methane isotopic signatures determined during near-source measurements Sara M. Defratyka https://data.mendeley.com/datasets/vfbbdvp9w2/1

Sara M. Defratyka, James L. France, Rebecca E. Fisher, Dave Lowry, Julianne M. Fernandez, Semra Bakkaloglu, Camille Yver-Kwok, Jean-Daniel Paris, Philippe Bousquet, Tim Arnold, Chris Rennick, Jon Helmore, Nigel Yarrow, and Euan G. Nisbet

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Short summary
We are focused on verification of δ13CH4 measurements in near-source conditions and we have provided an insight into the impact of chosen calculation methods for determined isotopic signatures. Our study offers a step forward for establishing an unified, robust, and reliable analytical technique to determine δ13CH4 of methane sources. Our recommended analytical approach reduces biases and uncertainties coming from measurement conditions, data clustering and various available fitting methods.