G01_P12

A sampling system for ¹⁴C analysis of atmospheric methane: from a laboratory prototype to an automated system.

Zazzeri G¹, Gautschi P¹, Graven H², Wacker L¹

¹ETH, Zürich, Switzerland, ²Imperial College London, London, United Kingdom

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 Imperial College London we developed a unique sampling system for ¹⁴C analysis of atmospheric CH₄ that addresses the sampling challenge, enabling extraction of carbon while sampling and collection of the air sample onto a small trap of molecular sieve (Zazzeri et al. 2021). This system is currently a laboratory prototype and technical developments are needed to make it portable and flexible to user need. The technical changes are being implemented at the Laboratory of Ion Beam Physics at ETH and include: 1) reducing the size of the system components to make the system fully portable, 2) making the sampling procedure fully automated, 3) interfacing the system with the gas ion source of the AMS system Micadas.

Here we present an overview of such developments, with a focus on the testing of a new molecular sieve sample trap. The new sample trap, with a smaller size than the one employed in the original system, will facilitate extraction of the collected carbon for ¹⁴C analysis and will enable direct interfacing with the gas ion source of the AMS system, making ¹⁴CH₄ measurements easier to perform.

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