Title Methane emissions from oil and gas platforms in the North Sea. Keywords Methane Production platforms Efficiency Field measurement Emission inventory Project description Currently, bottom-up methods estimate that 0.13 % of methane produced by UK North Sea oil and gas installations is lost. Here we measure emissions from eight platforms in the North Sea and, when considered collectively, the methane loss is estimated at 0.19 % of gas production. As this ambient loss is not explicitly accounted for in the bottom-up approach, these measured emissions represent significant additional emissions above previous estimates. The one file included in this digital repository is the original methane enhancement data for eight measurements around production platforms in the North Sea, UK, as described in Riddick et al. (2019) (submitted Feb 2019, accepted Jul 2019). Filename: acp-2019-90_data.txt Format: Tab delimited Text (.txt) Size: 32 KB Authors: Stuart Riddick; Denise Mauzerall Affiliation: Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544 Date: 18th July 2019 Contact: sriddick@princeton.edu; mauzerall@princeton.edu Project codes: US NOAA Grant # AWD1004141 UK NERC GAUGE project # NE/K002570/1 File header: Yes # of lines: 747 Header format: Name Format Description Date DD/MM/YYYY Date of measurement Time HH:MM:SS Time of measurement Lat Number (6 d.p) Latitude of measurement Lon Number (6 d.p) Longitude of measurement CH4_Enhancement Integer Methane enhancement above background (ppb) Riddick, S. N., Mauzerall, D. L., Celia, M., Harris, N. R. P., Allen, G., Pitt, J., Staunton-Sykes, J., Forster, G. L., Kang, M., Lowry, D., Nisbet, E. G., and Manning, A. J.: Measuring methane emissions from oil and gas platforms in the North Sea, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2019-90, in review, 2019. Abstract 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 off-loading 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 were 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.