Airborne in situ quantification of methane emissions from oil and gas production in Romania

Production of oil and gas in Romania, one of the largest producers in the European Union (EU), is associated with substantial emissions of methane to the atmosphere and may offer high emission mitigation potential to reach the climate objectives of the EU. However, comprehensive quantification of emissions in this area has been lacking. Here we report top-down emission rate estimates derived from aircraft-based in situ measurements that were carried out with two aircraft during the 2019 ROmanian Methane Emissions from Oil and gas (ROMEO) campaign, supported by simulations with atmospheric models. Estimates from mass balance flights at individual dense production clusters and around larger regions show large variations between the clusters, supporting the important role of individual super-emitters, and possibly show variable operation practices or maintenance states across the production basin. Estimated annual total emissions from the southern Romanian oil and gas (O&G) infrastructure are 227 +/- 86 kt CH4 yr-1, consistent with previously published estimates from ground-based site-level measurements during the same period. The comparison of individual plumes between measurements and atmospheric model simulations was complicated by unfavorable low-wind conditions. Similar correlations between measured and simulated CH4 enhancements during large-scale raster flights and mass balance flights suggest that the emission factor determined from a limited number of production clusters is representative of the larger regions. We conclude that ground-based and aerial emission rate estimates derived from the ROMEO campaign agree well, and the aircraft observations support the previously suggested large under-reporting of CH4 emissions from the Romanian O&G industry in 2019 to United Nations Framework Convention on Climate Change (UNFCCC). We also observed large underestimation from O&G emissions in the Emissions Database for Global Atmospheric Research (EDGAR) v7.0 for our domain of study.