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Mobile measurements help quantify and attribute methane emission sources in urban areas

7 December 2020

Methane is an important energy source in Europe, but also a strong greenhouse gas. Previous research in the United States has shown that new equipment detects considerably more gas leaks than equipment currently used by local gas utilities. This also appears to be the case in two European cities, Hamburg in Germany and Utrecht in the Netherlands, researchers write today in Atmospheric Chemistry and Physics.

Quantifying and attributing methane emissions to the atmosphere provides information for authorities and policymakers to design evidence-based climate policies. In urban areas methane can be produced from leaks in the gas pipeline networks, from microbial processes (e.g. the sewage or rain water drainage system) and from combustion processes. "By using mobile measurements with advanced technologies, we were able to detect, attribute, and quantify emissions from local sources from a driving vehicle." says Hossein Maazallahi, lead author of the study and PhD candidate at Utrecht University.

In both cities, the researchers found numerous methane enhancements of different magnitude (see figure below). But how can the production process be identified? "When methane is released from the natural gas network, we also see emission of ethane. Combustion-derived methane, on the other hand, is associated with large CO2 emissions, which we can also detect. When we see no ethane enhancement in detectable range, the methane comes from microbial processes. Furthermore, methane produced from the different sources also has a different isotopic composition, which independently confirms the source attribution." explains Maazallahi. By measuring the different tracers most of the observed methane elevations could be attributed to one of the three main categories.

"It turns out that the largest methane peaks in both cities originate from natural gas leaks, whereas many of the small leaks can come from the sewage system. Similar to what was found in US cities, a few large leaks appear to be responsible for a large fraction of the emissions. This means that finding and fixing these few large leaks quickly can significantly reduce methane emissions from cities." says project leader Thomas Röckmann, professor at Utrecht University. "Direct contact to the local gas utilities, STEDIN (Utrecht) and GasNetz Hamburg, helped to detect and repair several large leaks, although many of the smaller ones were not found/confirmed by the utilities." (https://av.tib.eu/media/49902).

The study highlights a feasible technology option that could be applied across Europe in collaboration with local utilities. "Gas network operators who modernize their leak detection system accordingly will not only protect the climate and thus ensure greater safety in the gas network, but can also make the detection of leaks more effective. The Hamburg operator, GasNetz Hamburg, has recognized this win–win situation and a follow-up study has already been started." says Stefan Schwietzke from the Environmental Defense Fund (EDF), which funded this study and similar studies in the US.

The measurements were carried out as part of the Marie Skłodowska-Curie Initial Training Network "Methane goes mobile – Measurements and Modelling project" (MEMO2, https://h2020-memo2.eu/) in collaboration with the Climate and Clean Air Coalition (CCAC) Oil and Gas Methane Science Studies, which were funded by the United Nations Environment Programme (UNEP), the Environmental Defense Fund (EDF), the European Commission, and the Oil and Gas Climate Initiative (OGCI).


The press release from the Environmental Defense Fund (EDF) can be found at: https://www.edf.org/media/scientists-discover-50-methane-leaks-city-hamburgs-gas-utility-network. The press release from Utrecht University can be found at: https://www.uu.nl/en/publicatie/scientists-discover-more-methane-leakages-in-utrechts-gas-distribution-network

Methane mapping, emission quantification, and attribution in two European cities: Utrecht (NL) and Hamburg (DE)
Maazallahi, H., Fernandez, J. M., Menoud, M., Zavala-Araiza, D., Weller, Z. D., Schwietzke, S., von Fischer, J. C., Denier van der Gon, H., and Röckmann, T.
Atmos. Chem. Phys., 20, 14717–14740, https://doi.org/10.5194/acp-20-14717-2020, 2020

Contact: Hossein Maazallahi (h.maazallahi@uu.nl)

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