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27-29 September 2023, University of Bayreuth (UBT)

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Clumped isotope laser spectroscopy of non-CO2 GHGs

Joachim Mohn1, Ivan Prokhorov1, Paul Magyar1, Noémy Chénier1, Lukas Emmenegger1, Béla Tuzson1
1 Laboratory for Air Pollution/Environmental Technology, Empa, 8600 Dübendorf, Switzerland

O 5.7 in Methods, Models, Standards

29.09.2023, 11:45-12:00, H 36

Abundances of doubly-substituted (i.e. clumped) isotopic species of non-CO2 greenhouse gases (GHGs) are novel tracers, especially in cases where the average (or bulk) isotopic composition is ambiguous. Under equilibrium conditions, they represent intra-species thermometers to trace the molecular temperature history. For kinetically controlled formation and removal processes, clumped isotopic signatures are linked to molecular mechanisms, reflecting reversibility or combinatorics, and can thus be applied to refine biogeochemical cycles. On the planetary scale, model predictions indicate that atmospheric measurements of clumped isotopic species provide constraints on trends in global source and sink magnitudes beyond current knowledge.

We present our recent advances in mid-IR quantum-cascade laser spectroscopy for rapid and high-precision analysis of 13CH3D and 12CH2D2 in methane (CH4) and 15N14N18O, 14N15N18O and 15N15N16O in nitrous oxide (N2O). Analytical developments include selection of spectral regions with improved selectivity, customization of spectrometers with inlet systems for automated sample dilution and injections, and referencing of measurements to stochastic distributions. The two laser spectrometers offer a rapid and precise approach for investigating various aspects of CH4 and N2O cycles and origins. Currently, we target first applications in the thermal history of methane-rich sedimentary rocks and key microbial formation pathways of nitrous oxide.

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