T03_P05

Direct graphitization of CO₂ from atmospheric air

Gautschi P¹, Wacker L¹, Synal H¹

¹ETH Zurich, Zurich, Switzerland

The atmospheric concentration of carbon dioxide (CO₂) is increasing rapidly since the industrialization. Emission of ¹⁴C free CO₂ from the combustion of fossil fuels, such as coal, oil or gas, reduces the ¹⁴CO₂ to ¹²CO₂ ratio in the atmosphere. When the background ¹⁴CO₂ level is known, the local surplus of fossil CO₂ in ppm can be calculated using the measured CO₂ concentration and the ¹⁴CO₂ abundance at a given sampling site.

A simple and fast method to prepare whole-air samples for radiocarbon analysis of atmospheric CO₂ has been developed and tested at ETH Zurich. Atmospheric air is collected in sampling bags (5 L) and then transported back to the laboratory, where CO₂ is isolated using the molecular sieve trap implemented in the automated graphitization line AGE3. The trapped CO₂ is then graphitized and measured by accelerator mass spectrometry (AMS).

A programmable air loading box to automatically collect and graphitize up to seven air samples at a time was constructed for reliable and repeatable results. A major benefit of the presented method is the reduced labour needed for sampling and graphitization. In a pilot study, twelve air samples were automatically collected within 1.5 days near the city of Zurich and later graphitized within another day.