14C analysis of atmospheric methane: development of a portable sampling system

Measurements of radiocarbon (¹⁴C) in atmospheric methane (CH₄) provide a powerful tool to distinguish fossil from biogenic methane emissions, because fossil methane is completely devoid of ¹⁴C. However, these measurements are particularly challenging as CH₄ is at low concentration in the atmosphere and large volumes of air must be sampled.

At the Laboratory of Ion Beam Physics (LIP), ETH, we developed a portable sampler based on the laboratory prototype in Zazzeri et al. 2021 [1]. The new system enables extraction of carbon from CH₄ while sampling in the field, reducing the sample processing in the laboratory and allowing collection of a hundred liters of air onto a 0.5 g zeolite trap.

Here we present an overview of the sampling system and the technical developments that have been implemented at LIP. The relatively small size of the sampler and its interface with the gas ion source of the AMS system make ¹⁴CH₄ measurements much easier to perform. Its portability will enable collection of CH₄ samples in any environment, with the potential of assessing the radiocarbon signature of methane emissions that have not been yet characterized.

[1] Zazzeri, G., Xu, X., & Graven, H. (2021). Environmental Science & Technology, 55(13), 8535-8541.