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Real-Time Monitoring of Methane Isotopes in Ambient Air

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Methane is one of the three most important greenhouse gases and is considered responsible for 20% of the observed enhanced greenhouse effect. In order to allow sensible emission mitigation strategies, accurate knowledge of methane’s emission sources and sinks is necessary. A valuable tool for distinguishing between emission sources is isotopic measurement. Within a sample, the relative concentrations of each methane isotopologue can vary significantly, as different sources and sinks of atmospheric methane can be either depleted or enriched in the heavier isotope. Methane of a biogenic origin, for example, is often depleted in the heavier isotopes due to the preference of life forms to utilise the lighter isotopes when taking in or expelling products. In contrast to this, non-biogenic sources, such as methane formation at high temperatures (eg. through combustion) are enriched in the heavier isotopes by varying degrees. The natural gas industry produces methane of variable isotopic composition, depending on the formation temperature of the gas reservoir. In this way, gas from Russian pipelines can be distinguished from that of the North Sea.

The objective of this project is to develop a highly sensitive cavity ring-down spectrometer for use in the real-time measurement of three stable methane isotopologues in ambient air; 12CH4, 13CH4 and CH3D. The acquisition of real-time, high-precision methane isotope data, when coupled with back-trajectory analysis, can help identify methane emissions by geographic location, time and source type. Such data will be of great benefit to atmospheric research and environmental monitoring.

This research project has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007 2013/ under REA grant agreement n° [331683].