London produces up to a third more methane than estimates suggest | Imperial News
Measurements of London‘s atmosphere show the city is releasing more methane, a potent greenhouse gas, mainly from natural gas leaks.
The measurements, made by researchers at Imperial College London, also show that most of the methane released in London is the result of leaks from natural gas infrastructure, rather than landfills as previously thought.
Methane is a more potent greenhouse gas than carbon dioxide and produces a stronger warming effect, but it stays in the atmosphere for a shorter time. Rising methane emissions around the world are a major concern and reducing them would help fight climate change.
Because we were able to identify the source of much of this additional methane, we have a clear direction to reduce emissions. Eric Saboya
The results of the new study, published in Chemistry and physics of the atmosphereshow that London’s natural gas infrastructure is leaking more methane than expected, and that the accumulation of many small leaks adds up to considerable additional methane emissions from the city.
Eric Saboya, first author of the study and student in the Science and Solutions for a Changing Planet doctoral training partnership, from Imperial’s Department of Physics, said: “Our study shows that London produces more methane than we do. thought, but because we were able to identify the source of much of this additional methane, we have a clear direction to reduce emissions.
“Previous estimates suggested that landfills in London were the biggest emitters of methane, but our study shows that natural gas leaks are a bigger problem. Mitigation strategies can now be directed where they are. the most needed, like upgrading old leaky metal pipes with new plastic versions.
Major sources of methane include agriculture, landfills and waste sites, natural gas infrastructure, and natural sources such as wetlands.
Methane emissions estimates are generally based on a “bottom-up” approach, where emissions have been calculated based on statistics. For example, cows produce methane, so knowing the average amount of methane produced by each cow and multiplying that by the number of cows in the UK gives an estimate of cow emissions for the whole country.
The new study instead used a ‘top-down’ approach of sampling the real atmosphere in London, from equipment installed at Imperial’s campus in South Kensington, to check whether the measurements were consistent with methane emissions. “ascending”.
Using continuous measurements from March 2018 to October 2020 and atmospheric transport models, the team compared bottom-up estimates with measured data. In addition to the concentration of methane in the local atmosphere, they were able to determine the source of the methane through small but measurable differences between the properties of methane from different sources.
Progress on pledges
These figures were compared to two “inventories” of emissions – bottom-up estimates. While one inventory (EDGAR) correlated relatively well with measurements of total methane concentration, the other (UK National Atmospheric Emissions Inventory, UK NAEI) appeared to underestimate methane emissions by 30-35%.
Both inventories underestimated the fraction of emissions from natural gas. For example, the NAEI inventory suggested that natural gas made up around 25% of the methane measured at South Kensington, while actual measurements show the reality is closer to 85%.
Study co-author Dr Giulia Zazzeri, from Imperial’s physics department, said: “It’s not just a London problem – cities like Paris and Boston have shown similar results – but the local composition of methane sources is different for each city, showing the power of these measures to determine where mitigation should be directed to help cities reduce their greenhouse gas emissions.
Study co-author Dr Heather Graven, from Imperial’s Department of Physics, added: “The UK was one of more than 100 countries that pledged to cut methane emissions. 30% by 2030 as part of the recent COP26 meeting in Glasgow. As methane is emitted from a variety of difficult-to-estimate sources, atmospheric measurements like these are key to tracking the UK’s progress on this commitment.
“Continuous CH4 and δ13CH4 Measurements in London Demonstrate Underreported Natural Gas Leaks” by Eric Saboya, Giulia Zazzeri, Heather Graven, Alistair J. Manning and Sylvia Englund Michel is published in Chemistry and physics of the atmosphere.