New developments in techniques for the sampling and analysis of atmospheric 14CO2 and 14CH4 at ETHZ and UNIBE, Switzerland

<p>Radiocarbon (¹⁴C) measurements of atmospheric greenhouse gases such as carbon dioxide (CO₂) and methane (CH₄) are central in our capability to identify their provenance. The ¹⁴C content of these gases provides more insight into the age of their sources and mainly allows the distinction between fossil and modern ones. ¹⁴CO₂ measurements can be used to analyze the nature of anthropogenic emissions (mostly fossil), or to discern on what organic matter pool respiration is taking place in a given environment. ¹⁴CH₄ can also be used to detect anthropogenic emissions (from leaks of natural gas, for example) as well as natural emissions produced by methanogenesis, for example from ruminants or in wetlands.</p> <p>The ¹⁴C analysis of atmospheric gases is made challenging due to their usual low concentration. Thus making the use of appropriate sampling methods, preconcentration and extraction techniques necessary to reach a sufficient amount of carbon for Accelerator Mass Spectrometry (AMS) analysis. We propose here a general view of the techniques that were developed at the Laboratory for Ion Beam Physics (ETHZ, Zurich), and at the Laboratory for the Analysis of Radiocarbon with AMS (UNIBE, Bern) for the purpose of analyzing CO₂ and CH₄ in atmospheric samples. We then discuss the practicability and the potential bias introduction of each of them.</p> <p>The techniques are as follows :</p> <ul> <li>Automated Graphitization Equipment with Automated Loading Facility (AGE-ALF)</li> <li>Automated Graphitization Equipment with Cryogenic Trap (AGE-CT)</li> <li>Methane Preconcentration and Purification System (MPPS)</li> </ul> <p>Generally, samples were collected in sampling bags, either in 5-15L capacity for CO₂ or larger than 60L for CH₄. Types of samples that are considered are atmospheric CO₂ and CH₄ samples, CO₂ from soil respiration, and CO₂ from cave air. The different techniques are presented, and ¹⁴C results from standard gases are compared between the extraction lines and two MICADAS AMS systems at ETHZ and UNIBE.</p>