London produces up to a third more methane than estimates suggest

Date:
February 17, 2022
Source:
Imperial College London
Summary:
Measurements of London's atmosphere show the city is releasing
more of the potent greenhouse gas methane, primarily from natural
gas leaks.



FULL STORY ========================================================================== Measurements of London's atmosphere show the city is releasing more of
the potent greenhouse gas methane, primarily from natural gas leaks.


==========================================================================
The measurements, performed by researchers at Imperial College London,
show that most methane released in London is the result of natural gas infrastructure leaks, rather than landfill sites 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 less
time. Methane emissions worldwide are a major concern and reducing them
would help tackle climate change.

The results of the new study, published in Atmospheric Chemistry and
Physics, show London's natural gas infrastructure is leaking more methane
than estimated, and the cumulation of lots of small leaks is adding up
to considerable extra methane emissions from the city.

First author of the study and Science and Solutions for a Changing Planet Doctoral Training Partnership student Eric Saboya, from the Department
of Physics at Imperial, said: "Our study shows that London is emitting
more methane than we thought, but because we've been able to pinpoint
the source of much of this extra methane, we have a clear direction to
reduce emissions.

"Previous estimates suggested that landfill sites 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 most needed, such as upgrading leaky old metal pipes with
newer plastic versions." Major sources of methane include agriculture, landfill and waste sites, natural gas infrastructure and natural sources
such as wetlands.



========================================================================== Estimates of methane emissions are typically based on a 'bottom-up'
approach, where emissions were calculated based on statistics. For
example, cows produce some methane, so knowing on average how much methane
each cow produces and multiplying this by the number of cows in the UK
gives an estimate of the emissions from cows for the country as a whole.

The new study instead used a 'top-down' approach of sampling the
actual atmosphere in London, from equipment installed on Imperial's
South Kensington campus, to check if the measurements agreed with the 'bottom-up' methane emissions.

Using continuous measurements from March 2018 to October 2020 and models
of atmospheric transport, the team compared bottom-up estimates with
the measured data. As well as the concentration of methane in the local atmosphere, they were able to tell the source of the methane thanks to
small but measurable differences between the properties of methane from different sources.

These figures were compared to two emissions 'inventories' -- bottom-up estimates. While one inventory (EDGAR) correlated relatively well with
the measurements in 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 natural gas accounted for
around 25% of the methane measured in South Kensington, whereas the real measurements show the reality is closer to 85%.

Study co-author Dr Giulia Zazzeri, from the Department of Physics at
Imperial, said: "This is not just a London problem -- cities such
as Paris and Boston have shown similar results -- but the local
make-up of methane sources is different for every city, showing the
power of these measurements for determining where mitigation should
be directed to help cities reduce their greenhouse gas emissions."
Study co-author Dr Heather Graven, from the Department of Physics at
Imperial, added: "The UK was one of over 100 countries who pledged
to reduce methane emissions 30% by 2030 as part of the recent
COP26 meeting in Glasgow. Since methane is emitted by various
sources that are difficult to estimate, atmospheric measurements
like these are key to tracking the UK's progress on this pledge."
special promotion Explore the latest scientific research on sleep and
dreams in this free online course from New Scientist -- Sign_up_now_>>> ========================================================================== Story Source: Materials provided by Imperial_College_London. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Eric Saboya, Giulia Zazzeri, Heather Graven, Alistair J. Manning,
and
Sylvia Englund Michel. Continuous CH4 and d13CH4 measurements in
London demonstrate under-reported natural gas leakage. Atmospheric
Chemistry and Physics (preprint link), 2022 [abstract] ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220217141231.htm

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