Preprints
https://doi.org/10.5194/acp-2020-1099
https://doi.org/10.5194/acp-2020-1099

  22 Oct 2020

22 Oct 2020

Review status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Speciation of VOC emissions related to offshore North Sea oil and gas production

Shona E. Wilde1, Pamela A. Dominutti1,2, Stephen J. Andrews1, Stephane J.-B. Bauguitte5, Ralph R. Burton4, Ioana Colfescu4, James France6,7, James R. Hopkins1,3, Anna E. Jones6, Tom Lachlan-Cope6, James D. Lee1,3, Alastair C. Lewis1,3, Stephen D. Mobbs4, Alexandra Weiss6, Stuart Young1, and Ruth M. Purvis1,3 Shona E. Wilde et al.
  • 1Wolfson Atmospheric Chemistry Laboratories, University of York, York, YO10 5DD, UK
  • 2Laboratoire de Météorologie Physique, University of Clermont Auvergne, 63000, Clermont-Ferrand, France
  • 3National Centre for Atmospheric Science, University of York, York, YO10 5DD, UK
  • 4National Centre for Atmospheric Science, School of Earth and Environment, University of Leeds, LS2 9JT, UK
  • 5Facility for Airborne Atmospheric Measurements, Cranfield University, Bedford, UK
  • 6British Antarctic Survey, Natural Environment Research Council, Cambridge CB3 0ET, UK
  • 7Department of Earth Sciences, Royal Holloway, University of London, Egham TW20 0EX, UK

Abstract. The North Sea is Europe's key oil and gas (O&G) basin with the output currently meeting 3–4 % of global oil supply. Despite this, there are few observational constraints on the nature of atmospheric emissions from this region, with most information derived from bottom-up inventory estimates. This study reports on airborne measurements of volatile organic compounds (VOCs) emitted from O&G producing regions in the North Sea. VOC source emission signatures for the primary extraction products from offshore fields (oil, gas, condensate, mixed) were determined in four geographic regions. Measured iso-pentane to n-pentane (iC5 / nC5) ratios were 0.89–1.24 for all regions, used as a confirmatory indicator of O&G activities. Light alkanes (ethane, propane, butane, pentane) were the dominant species emitted in all four regions, however total OH reactivity was dominated by unsaturated species, such as 1,3-butadiene, despite their relatively low abundance. Benzene to toluene ratios indicated the influence of possible terrestrial combustion sources of emissions in the southern, gas-producing region of the North Sea, seen only during south or south-westerly wind episodes. However, all other regions showed a characteristic signature of O&G operations. Correlations between ethane (C2H6) and methane (CH4), confirmed O&G production to be the primary CH4 source. The enhancement ratio (ΔC2H6 / ΔCH4) ranged between 0.03–0.18, indicating a spatial dependence on emissions with both wet and dry CH4 emission sources. The excess mole fraction demonstrated that deepwater oil extraction resulted in a greater proportion of emissions of higher carbon number alkanes relative to CH4, whereas gas extraction, typically from shallow waters, resulted in a less complex mix of emissions dominated by CH4. The VOC source profiles measured were similar to those in the UK National Atmospheric Emissions Inventory (NAEI) for oil production, with consistency between the molar ratios of light alkanes to propane. The largest discrepancies between observations and the inventory were for mono-aromatic compounds, highlighting that these species are not currently fully captured in the inventory. These results demonstrate the applicability of VOC measurements to distinguish unique sources within the O&G sector and give an overview of VOC speciation over the North Sea.

Shona E. Wilde et al.

 
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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Shona E. Wilde et al.

Shona E. Wilde et al.

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Short summary
We use airborne measurements to evaluate the speciation of volatile organic compound (VOC) emissions from offshore oil and gas (O&G) installations in the North Sea. The composition of emissions varied across regions associated with either gas, condensate or oil extraction, demonstrating that VOC emissions are not uniform across the whole O&G sector. We compare our results to VOC source profiles in the UK emissions inventory, showing these emissions are not currently fully characterised.
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