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  • Periodic Reporting for period 1 - ISOMET (Atmospheric content of the most abundant of 12CH4 isotopologues from ground-based and satellite infrared solar observations and development of a methane isotopic GEOS-Chem module.)

ISOMET Report Summary

Project ID: 704951
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - ISOMET (Atmospheric content of the most abundant of 12CH4 isotopologues from ground-based and satellite infrared solar observations and development of a methane isotopic GEOS-Chem module.)

Reporting period: 2016-10-01 to 2017-09-30

Summary of the context and overall objectives of the project

Atmospheric methane, the second most important greenhouse gas emitted by human activities, is responsible for approximately one fifth of the changes in the Earth’s balance energy since the beginning of the industrialization (~1750). Methane concentrations have reached a new high of 1845 ppb in 2016 with a renewed rise in the last decade after a period of stabilization between 1999 and 2006. To this day, the source or sink responsible of the latest increase remains unexplained.

Depending on the emission process, heavy molecules of methane (13CH4 and CH3D), called isotopologues, are emitted along methane with specific emission ratios. Despite their small relative abundances of 110 and 60 000 respectively, they give therefore crucial information on the concentration of methane in the atmosphere and its evolution. Determining the isotopic ratio of atmospheric methane is therefore a unique tracer of its budget. In a context of an urgency for climate change mitigation, understanding the evolution of a major greenhouse gas is of crucial importance.

To this day, no study of the isotopic ratio of methane derived from ground-based solar observations has been published. Measurements of heavy methane from Fourier Transform InfraRed spectra will help fill this gap. This project focuses on developing a retrieval strategy from observations recorded with state of the art spectrometers installed at Eureka [Arctic, Canada], Toronto [Ontario, Canada] and Jungfraujoch [Switzerland] in the framework of the Network for Detection of Atmospheric Composition Change ( These newly produced time series will ease data interpretation and contribute to a global view of the question of isotopologues, and therefore atmospheric methane.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Through the first year of this project, we developed a retrieval strategy for CH3D through the identification of the best combination of available parameters in order to minimize errors and maximize the vertical sensitivity range. The development of the retrieval strategy for 13CH4 is in the finalization phase while the CH3D time series is undergoing quality control (preliminary CH3D total column time series for Eureka and Toronto are displayed in attached figures).

Preliminary tests of the developed retrieval strategy for CH3D have been performed for the first time for observations collected at the following additional NDACC observations sites: Portovelho [Brasil], Saint-Denis [Réunion Island], Maido [Réunion Island], and Lauder [New Zealand].

With this newly developed strategy we aim to retrieve CH3D with a vertical sensitivity range allowing us to produce, in addition to total columns, a tropospheric and a stratospheric partial column time series. Those results will enable us to perform consistent dataset intercomparisons, respectively between FTIR tropospheric partial columns and in situ surface measurements, and FTIR stratospheric partial columns and ACE-FTS satellite observations.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

This project allows for first long term measurements of heavy methane from infrared ground-based solar observations. By reaching out to various atmospheric composition measurement and modelling scientific teams, this project raises interest in the question of atmospheric methane increase through a new and innovative angle. Improving our knowledge in the budget of the second most important greenhouse gas through international collaborations and with different research communities is at the forefront of climate change studies.

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