Comment on acp-2022-679

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Gas flaring is a substantial global source of carbon emissions to atmosphere and is targeted as a route to mitigating the oil and gas sector carbon footprint due to the waste of resources involved. However, quantifying carbon emissions from flaring is resource-intensive, and no studies have yet assessed flaring emissions for offshore regions. In this work, we present carbon dioxide (<span class="inline-formula">CO₂</span>), methane (<span class="inline-formula">CH₄</span>), ethane (<span class="inline-formula">C₂H₆</span>), and <span class="inline-formula">NO_<i>x</i></span> (nitrogen oxide) data from 58 emission plumes identified as gas flaring, measured during aircraft campaigns over the North Sea (UK and Norway) in 2018 and 2019. Median combustion efficiency, the efficiency with which carbon in the flared gas is converted to <span class="inline-formula">CO₂</span> in the emission plume, was 98.4 % when accounting for <span class="inline-formula">C₂H₆</span> or 98.7 % when only accounting for <span class="inline-formula">CH₄</span>. Higher combustion efficiencies were measured in the Norwegian sector of the North Sea compared with the UK sector. Destruction removal efficiencies (DREs), the efficiency with which an individual species is combusted, were 98.5 % for <span class="inline-formula">CH₄</span> and 97.9 % for <span class="inline-formula">C₂H₆</span>. Median <span class="inline-formula">NO_<i>x</i></span> emission ratios were measured to be 0.003 <span class="inline-formula">ppm ppm^−1 CO₂</span> and 0.26 <span class="inline-formula">ppm ppm^−1 CH₄</span>, and the median <span class="inline-formula">C₂H₆:CH₄</span> ratio was measured to be 0.11 <span class="inline-formula">ppm ppm^−1</span>. The highest <span class="inline-formula">NO_<i>x</i></span> emission ratios were observed from floating production storage and offloading (FPSO) vessels, although this could potentially be due to the presence of alternative <span class="inline-formula">NO_<i>x</i></span> sources on board, such as diesel generators. The measurements in this work were used to estimate total emissions from the North Sea from gas flaring of 1.4 <span class="inline-formula">Tg yr^−1</span> <span class="inline-formula">CO₂</span>, 6.3 <span class="inline-formula">Gg yr^−1</span> <span class="inline-formula">CH₄</span>, 1.7 <span class="inline-formula">Gg yr^−1</span> <span class="inline-formula">C₂H₆</span> and 3.9 <span class="inline-formula">Gg yr^−1</span> <span class="inline-formula">NO_<i>x</i></span>.