Fugitive Methane Detection from UK Above Ground Gas Infrastructure

Methane is a powerful greenhouse gas with a globally averaged atmospheric mole fraction of 1908±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).  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°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 CH₄ reductions, with the UN stating that an emissions reduction of 61% is possible, but there is now urgent need to implement this (Nisbet et al, 2019).

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 et al., 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.

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 (δ¹³C) at different points in the gas distribution supply chain. The range of signatures identified is from -43.7 to -32.4 ‰ (n=182), showing an enrichment relative to atmospheric background (-48 to -47.5‰), with the southern North Sea production that feeds into the Bacton Terminal identified as the most enriched at -31.8 ±1.5‰ (n=13).

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 et al, 2015: Lowry et al, 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.

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.

 

France et al., 2021, Atmos. Meas. Tech., 14, 71–88, 10.5194/amt-14-71-2021

Lowry et al., 2020, Science of the Total Environ., 708, 134600, 10.1016/j.scitotenv.2019.134600

Nisbet et al., 2019., Global Biogeochem. Cycles, 33, 25pp, 10.1029/2018GB006009 

Rella et al., 2015., Atmos. Meas. Tech., 8, 4539–4559, 10.5194/amt-8-4539-2015.

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)