Browsing by Author "Nisbet, Euan"
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Item Open Access Estimating the size of a methane emission point source at different scales: from local to landscape(European Geosciences Union (EGU) / Copernicus Publications, 2017-06-29) Riddick, Stuart N.; Connors, Sarah; Robinson, Andrew D.; Manning, Alistair J.; Jones, Pippa S. D.; Lowry, David; Nisbet, Euan; Skelton, Robert L.; Allen, Grant; Pitt, Joseph; Harris, Neil R. P.High methane (CH4) mixing ratios (up to 4 ppm) have occurred sporadically at our measurement site in Haddenham, Cambridgeshire, since July 2012. Isotopic measurements and back trajectories show that the source is the Waterbeach Waste Management Park 7 km SE of Haddenham. To investigate this further, measurements were made on 30 June and 1 July 2015 at other locations nearer to the source. Landfill emissions have been estimated using three different approaches at different scales; near source using the WindTrax inversion dispersion model, middle distance using a Gaussian plume (GP) model and at the landscape scale using the Numerical Atmospheric Modelling Environment (NAME) Inversion Technique for Emission Modelling (InTEM) inversion. The emission estimates derived using the WindTrax and Gaussian plume (GP) approaches agree well for the period of intense observations. Applying the Gaussian plume approach to all periods of elevated measurements seen at Haddenham produces year-round and monthly landfill emission estimates with an estimated annual emission of 11.6 GgCH(4) yr(-1). The monthly emission estimates are highest in winter (2160 kg h(-1) in February) and lowest in summer (620 kg h(-1) in July). These data identify the effects of environmental conditions on landfill CH4 production and highlight the importance of year-round measurements to capture seasonal variability in CH4 emission.Item Open Access Estimating the size of a methane emission point-source at different scales: from local to landscape(Copernicus Publications, 2016-11-22) Riddick, Stuart N.; Connors, Sarah; Robinson, Andrew D.; Manning, Alistair J.; Jones, Pippa S. D.; Lowry, David; Nisbet, Euan; Skelton, Robert L.; Allen, Grant; Pitt, Joseph; Harris, Neil R. P.High methane (CH4) mixing ratios (up to 4 ppm) have occurred sporadically at our measurement site in Haddenham, Cambridgeshire since July 2012. Isotopic measurements and back trajectories show that the source is the Waterbeach Waste management park 7 km SE of Haddenham. To investigate this further, measurements were made on June 30th and July 1st 2015 at other locations nearer to the source. Landfill emissions have been estimated using three different approaches (WindTrax, Gaussian plume, and NAME InTEM inversion) applied to the measurements made close to source and at Haddenham. The emission estimates derived using the WindTrax and Gaussian plume approaches agree well for the period of intense observations. Applying the Gaussian plume approach to all periods of elevated measurements seen at Haddenham produces year-round and monthly landfill emission estimates. The estimated annual emissions vary between 11.6 and 13.7 Gg CH4 yr−1. The monthly emission estimates are highest in winter (2160 kg hr−1 in February) and lowest in summer (620 kg hr−1 in July). These data identify the effects of environmental conditions on landfill CH4 production and highlight the importance of year-round measurement to capture seasonal variability in CH4 emission. We suggest the landscape inverse modelling approach described in this paper is in good agreement with more labour-intensive near-source approaches and can be used to identify point-sources within an emission landscape to provide high-quality emission estimates.Item Open Access Measuring methane emissions from oil and gas platforms in the North Sea(European Geosciences Union (EGU) / Copernicus Publications, 2019-08-02) Riddick, Stuart N.; Mauzerall, Denise L.; Celia, Michael; Harris, Neil R. P.; Allen, Grant; Pitt, Joseph; Staunton-Sykes, John; Forster, Grant L.; Kang, Mary; Lowry, David; Nisbet, Euan; Manning, Alistair J.Since 1850 the concentration of atmospheric methane (CH4), a potent greenhouse gas, has more than doubled. Recent studies suggest that emission inventories may be missing sources and underestimating emissions. To investigate whether offshore oil and gas platforms leak CH4 during normal operation, we measured CH4 mole fractions around eight oil and gas production platforms in the North Sea which were neither flaring gas nor offloading oil. We use the measurements from summer 2017, along with meteorological data, in a Gaussian plume model to estimate CH4 emissions from each platform. We find CH4 mole fractions of between 11 and 370 ppb above background concentrations downwind of the platforms measured, corresponding to a median CH4 emission of 6.8 g CH4 s−1 for each platform, with a range of 2.9 to 22.3 g CH4 s−1. When matched to production records, during our measurements individual platforms lost between 0.04 % and 1.4 % of gas produced with a median loss of 0.23 %. When the measured platforms are considered collectively (i.e. the sum of platforms' emission fluxes weighted by the sum of the platforms' production), we estimate the CH4 loss to be 0.19 % of gas production. These estimates are substantially higher than the emissions most recently reported to the National Atmospheric Emission Inventory (NAEI) for total CH4 loss from United Kingdom platforms in the North Sea. The NAEI reports CH4 losses from the offshore oil and gas platforms we measured to be 0.13 % of gas production, with most of their emissions coming from gas flaring and offshore oil loading, neither of which was taking place at the time of our measurements. All oil and gas platforms we observed were found to leak CH4 during normal operation, and much of this leakage has not been included in UK emission inventories. Further research is required to accurately determine total CH4 leakage from all offshore oil and gas operations and to properly include the leakage in national and international emission inventories.