Isotopic signatures of methane emission from oil and natural gas plants in southwestern China

Abstract. Methane (CH₄) emissions to atmosphere from Chinese oil and gas (ONG) sector are subject to considerable uncertainty. The isotopic composition of CH₄ isotopes (δ¹³C) varies between emission sources, enabling the identification of changes in specific CH₄ sources. However, there are few relevant studies in China, especially at the ONG site level. We obtained CH₄ mixing ratios and isotopes from atmospheric samples collected by UAV and ground monitoring, and employed the HYSPLIT model to investigate CH₄ distribution at ONG sites in southwest China. It was found that the CH₄ isotopic signatures provide a strong basis for the emission intensity at the ONG sites. The meteorological and site conditions were identified as the most influential factors in CH₄ distribution at sites. The CH₄ from the equipment area contributed approximately a quarter of the CH₄ observed over the sites. The CH₄ source isotopic signatures (δ¹³C) of this study were heavier than those globally, indicating that they were mainly thermogenic sources. Finally, the heavier δ¹³C of this region may lead to an overestimation emission of global CH₄ from fossil fuel sources by 3.47 Tg CH₄ yr^-1, and underestimation from microbial sources. This study highlights the importance of regional CH₄ isotopes, with great significance for CH₄ inventories of global sectors.