Fugitive Methane Detection from UK Above Ground Gas Infrastructure

<p>Methane is a powerful greenhouse gas with a globally averaged atmospheric mole fraction of 1908&#177;2 ppb in 2021, nearly three times the pre-industrial abundance. The annual increase of methane between 2020 and 2021 was the highest since continuous measurement began (WMO,2022). &#160;More than 60% of global CH₄ emissions are attributed to human activities. Reducing methane in the short term will help to achieve the Paris Agreement goal to keep warming to <1.5&#176;C and help in reaching many Sustainable Development Goals due to multiple co-benefits of methane mitigation. The fossil fuel sector is one of the largest anthropogenic emitters of methane and a target for CH₄reductions, with the UN stating that an emissions reduction of 61% is possible, but there is now urgent need to implement this (Nisbet <em>et al</em>, 2019).</p> <p>Sources of fugitive methane emissions in the UK have been identified and characterized by mobile measurement survey in vehicles (e.g. Lowry et al ,2020) and aircraft (e.g. France <em>et al</em>., 2021). Since 2017, vehicles surveys for UN and NERC-UK projects have identified emissions from production platforms, onshore terminals, compressor stations, offtake stations, gas governors and pipeline failures.</p> <p>Vehicle surveys utilized different suites of instruments: Picarro G2301 and G2210-i Los Gatos Research Ultraportable Methane-Ethane (LGR UMEA), and LiCor 7810 GHG analyzers, all measuring methane. Air bags were filled in plumes during surveys to measure the carbon isotopic signature (&#948;¹³C) at different points in the gas distribution supply chain. The range of signatures identified is from -43.7 to -32.4 &#8240; (n=182), showing an enrichment relative to atmospheric background (-48 to -47.5&#8240;), with the southern North Sea production that feeds into the Bacton Terminal identified as the most enriched at -31.8 &#177;1.5&#8240; (n=13).</p> <p>Ethane:methane ratio is a useful diagnostic for gas attribution. Since 2018 the LGR UMEA ethane data has been used to identify distribution leaks as this gas is not a component of waste, agricultural or coal sources. The ratio of C₂H₆:CH₄ (C2:C1) during surveys of gas allows separation of pyrogenic and thermogenic (>0.03) from biogenic (<0.005) sources (Rella <em>et al</em>, 2015: Lowry <em>et al</em>, 2020), with UK gas distribution dominantly in the range 0.04 to 0.08, and it is consistent for fugitive plumes transected on multiple passes.</p> <p>Most of the larger peaks have been located downwind of offtake stations on the high-pressure mains network. The 2021 surveys focused on identification of emitting facilities and their isotopic and C2:C1 characterization. Recent surveys in 2022 targeted emission plumes for multiple passes with 10Hz and 1Hz instruments to select suitable candidates for Gaussian plume emission modelling, with potential to upscale to a national emission for facilities of this category.</p> <p>&#160;</p> <p>France <em>et al</em>., 2021, Atmos. Meas. Tech., 14, 71&#8211;88, 10.5194/amt-14-71-2021</p> <p>Lowry <em>et al</em>., 2020, Science of the Total Environ., 708, 134600, 10.1016/j.scitotenv.2019.134600</p> <p>Nisbet <em>et al</em>., 2019., Global Biogeochem. Cycles, 33, 25pp, 10.1029/2018GB006009&#160;</p> <p>Rella et al., 2015., Atmos. Meas. Tech., 8, 4539&#8211;4559, 10.5194/amt-8-4539-2015.</p> <p>World Meteorological Organisation, 2022. (WMO) greenhouse gas bulletin. [Online]. Available at: https://public.wmo.int/en/resources/library/wmo-greenhouse-gas-bulletin. (Accessed 9 December 2022)</p>