A breath of fresh air: sampling of δ13C and δ2H methane isotopes becomes simultaneous and automated

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  • Published: Jul 15, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: Gas Chromatography
thumbnail image: A breath of fresh air: sampling of δ13C and δ2H methane isotopes becomes simultaneous and automated

Anthropocene

Humanity has massively overdrawn its methane budget so the international community has agreed to take drastic action.

December 12, 2015 was a historic day. In an industrious suburb north east of Paris, delegates representing 195 nations, sleep deprived from two gruelling weeks of intense discussions and negotiations, principally agreed to curb humans’ impact on the world. Their aim was to limit global warming to less than 2°C above the temperatures experienced by our 18th century pre-industrial ancestors. How? By cutting the amount of greenhouse gas we release into the atmosphere.

As of the turn of the second millennium, our atmosphere had three times the amount of methane gas that it had before the Industrial Revolution. ‘The present rate of increase, between 5 and 10 ppb/year,’ Brand and colleagues explain in Rapid Communications in Mass Spectrometry,’…has made methane a major focus of interest in climate change mitigation scenarios.’ Furthermore, since methane remains in the atmosphere for roughly 12 years, its potential for causing global warming is 25-fold greater than that of CO2.

A so-called greenhouse gas, methane is notorious for hoarding infrared radiation from cosmic rays, warming our planet in the process. Human destruction of forests, our massive reliance on ruminant animals (cows, sheep, etc.) and coal mining, and the knock-on melting of the permafrost all contribute to our methane budget; a budget that we have massively overdrawn. We have manufactured our increasingly inhospitable world and thus it is our problem to deal with.

Methane budget

Just like a less-than-impressed bank manager, scientists are developing tools to monitor our total methane expenditure and to track the source of our bad habits. ‘Most of these sources produce methane of different isotopic signatures, both in δ13C values and in δ2H values,’ the authors explain. ‘…the flux-variation of different methane sources can be distinguished by isotopic measurements.’ Furthermore, these flux variations have the potential to inform us on the reduction of atmospheric methane by OH radicals, aiding climate scientists in fine tuning their atmospheric models.

To achieve this, however, researchers must address this problem: current techniques require large air volumes—a logistical nightmare and much more than glacial samples can realistically provide—just to sample the near-trace amounts of methane. Furthermore, to sample both δ13C and δ2H methane isotopes, twice the amount of sample is needed.

Spurred on by these challenges, collaborators from the Max-Planck Institute for Biogeochemistry, Germany, and the National Institute of Water and Atmospheric Research, New Zealand, worked together to develop a fully automated system capable of sampling methane isotopes with just 200 mL of air. This, they hoped, would relieve the high throughput demands placed on Max-Planck’s sampling station.

Bespoke

The team of scientists fashioned a bespoke ‘multi-cryo trap/GC/isotope ratio MS’ system using both commercially available and DIY components. First of all, trace amounts of methane were plucked from the air and concentrated within six cryotraps, packed with Hayesep D absorption polymer, and then cooled at -130°C.

Residual air components—nitrogen, oxygen, argon, carbon monoxide, and krypton, for example—were further separated from methane by GC with two custom-made Shincarbon-ST stationary phases. Finally, volatilised air components were fed directly into one of two stable isotope ratio mass spectrometers. The first, charmingly named ‘Chiara’, measured the isotopes of CO2 (and particularly those from methane), whilst the second, ‘Diana’, sampled any hydrogen isotopes of methane.

Having achieved the fully automated and simultaneous analyses of carbon and hydrogen methane isotopes for the first time, the authors briefly touch on their sampling of methane isotopes in the air obtained over three years since July 2012. The ‘δ13C values seem to decrease over time at a rate of -7 × 10-5 per day,’ the paper notes, ‘which amounts to -0.07% in 3 years.’ Principally, the 2015 Paris Agreement doesn’t come into effect until 2020 and given the novelty of this technique such data should be taken with a pinch of salt, for the time being at least. The authors intend to follow up with full data in a separate publication in due course.

Related Links

Rapid Commun. Mass Spectrom., 2016, 30, 1523-1539. Brand et al. Automated simultaneous measurement of the δ13C and δ2H values of methane and the δ13C and δ18O values of carbon dioxide in flask air samples using a new multi cryo-trap/gas chromatography/isotope ratio mass spectrometry system.

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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