CH4 isotopic signatures of emissions from oil and gas extraction sites in Romania

Dataset linked to the manuscript "CH4 isotopic signatures of emissions from oil and gas extraction sites in Romania", submitted to Elementa: Science of the Anthropocene. Abstract: Methane (CH4) emissions to the atmosphere from the oil and gas sector in Romania remain highly uncertain, despite their relevance for the European Union’s goals to reduce greenhouse gas emissions. Measurements of the isotopic composition of CH4 can be used for source attribution, which is important in top-down studies of emissions from extended areas. We performed isotope measurements of CH4 in atmospheric air samples collected from an aircraft (24 locations) and ground vehicles (83 locations), around oil and gas production sites in Romania, with focus on the Romanian Plain. Ethane to methane ratios (C2:C1) were derived at 412 locations of the same fossil fuel activity clusters. The resulting isotopic signals (δ13C and δ2H in CH4) covered a wide range of values, indicating mainly thermogenic gas sources (associated with oil production) in the Romanian Plain, mostly in Prahova county (δ13C from -67.8 to -22.4 per mille V-PDB; δ2H from -255 to -138 per mille V-SMOW) but also the presence of some natural gas reservoirs of microbial origin in Dolj, Ialomia, Prahova and likely Teleorman counties. The classification based on C2:C1 ratios was generally in agreement with the one based on CH4 isotopic composition, and confirmed the characterisation of the gas origin. In several cases, the CH4 enhancements sampled from the aircraft could directly be linked to the underlying production clusters using wind data. The combination of δ13C and δ2H signals determined on these samples confirm that the oil and gas production sector is the main source of CH4 emissions in the target areas.