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Observation and Modelling of Radiocarbon in Atmospheric Methane for Methane Source Identification

Periodic Reporting for period 4 - METHID (Observation and Modelling of Radiocarbon in Atmospheric Methane for Methane Source Identification)

Okres sprawozdawczy: 2020-12-01 do 2022-05-31

Emissions of methane (CH4) are the 2nd largest contributor to global climate change, but the attribution of emissions to specific sources, such as natural gas leaks, landfills or livestock, currently has large uncertainties. This project advanced the state-of-the-art for characterisation of anthropogenic sources of CH4 with the use of radiocarbon and it created new directions in atmospheric methane research, with the potential to impact global climate policy and industrial practices over the next 10-20 years.

We developed an innovative new technique to sample atmospheric CH4 for radiocarbon analysis that simplifies and improves upon previous methods (WP1). Radiocarbon measurements in atmospheric CH4 (14CH4) can identify fossil fuel emissions because radiocarbon is absent in fossil fuel CH4 (from natural gas, coal) but present in biogenic CH4 (waste, livestock). However, it is challenging to perform 14CH4 measurements using current techniques. Our new technique has been proven and applied to measure 14CH4 in London, providing the first quantitative regional assessment of fossil CH4 emissions using 14CH4 and showing strong fossil CH4 emissions in London. The technique is now being developed into a portable, automatic system that can be easily used by other researchers, as part of a Marie Curie fellowship by one of the team members.

By close examination of nuclear reactor design and operation, we have produced improved estimates of 14CH4 emissions from nuclear power plants, which can interfere with the 14CH4 tracer technique (WP2). We have developed the first 3-dimensional modelling of 14C in CH4 at regional and global scales to enable the application of 14CH4 observations to estimate the fossil fraction of global and regional CH4 emissions (WP3 and WP4). We have conducted a multi-tracer analysis of the global CH4 budget that incorporates multiple constraints as well as uncertainties that have previously been neglected, leading to biases in prior work.

Major outcomes of this project are the introduction and deployment of new approaches to identify fossil vs biogenic CH4 emissions, validate CH4 emissions mitigation policies and understand the response of wetland ecosystems to climate change.
The project team has performed work on the work packages 1-5, encompassing laboratory development, analysis of nuclear power plant emissions, atmospheric measurements and regional and global modelling of radiocarbon in methane. There have been four papers published, one is in review, and three more are in preparation. There have been multiple conference presentations and several presentations to the public and policymakers about the project (Imperial ERC 10th Anniversary Event, Imperial Fringe Event “Walking in the Air”, Imperial Physics Alumni visit and laboratory tours, and a presentation to civil servants in UK Government).
The paper published in Radiocarbon in 2018 provides estimates of 14CH4 and 14CO2 emissions from all nuclear power plants over 1971-2016. It conducts a detailed assessment of the emission factors (emissions per unit power produced) for nuclear power plants in Europe.

The paper published in Earth’s Future lays out, for the first time, an approach for interpreting observations of radiocarbon in methane to determine fossil fuel and biogenic sources on regional scales. It demonstrates the expected regional signals and their utility using atmospheric transport simulations using the region of California as a test case.

The paper published in Environmental Science and Technology demonstrates the novel, efficient new technique for sampling atmospheric methane for radiocarbon analysis that we developed. The new technique collects methane carbon at the point of sampling, minimizing the subsequent laboratory processing needed and eliminating the need to pressurize and ship hazardous goods. The new technique is also more precise than other recent measurements. The prototype system is presently being developed into a portable, automatic system that can be used by other researchers.

The paper published in Atmospheric Chemistry and Physics demonstrates that natural gas leaks in London are being underestimated, using observations made at our laboratory enabled by the ERC project. A press release accompanied the publication and a briefing note is currently being prepared for the Greater London Authority.

A paper in review uses prior measurements of radiocarbon and other methane isotopes to revisit the global methane budget. It concludes that anthropogenic fossil sources of methane are likely not underestimated globally, in contrast to recent isotope-based studies. This result is critical to the development of effective policies to meet the Paris Agreement and the Global Methane Pledge.
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