[A-AS11] Atmospheric Chemistry

[AAS11-05] Declining Methane Leakage from Oil & Gas: Uncovered by Atmospheric Observation in Western Siberia

*Takuto Taguchi¹, Motoki Sasakawa¹, Toshinobu Machida¹, Qianning Qin¹, Aleksandr Nogovitcyn¹, Masayuki Kondo² (1.National Institute for Environmental Studies, 2.The IDEC Institute, Hiroshima University)

Keywords:Methane Leakage, Western Siberia, JR-STATION

Methane (CH₄) emissions from the oil and gas (O&G) sectors represent a significant contribution to the atmospheric burden, accounting for approximately 25 % of anthropogenic CH₄ emissions. Russia plays a significant role as the second-largest contributor (following the USA) to CH₄ emissions; however, there is uncertainty in the estimates provided by inventories (Bottom-Up: BU) and atmospheric inverse models (Top-Down: TD), as well as discrepancies in trends (decreasing for BU and increasing for TD). The National Institute for Environmental Studies (NIES) has been carrying out continuous atmospheric measurements of CH₄ and CO₂ concentrations using an expanding network of towers known as the Japan–Russia Siberian Tall Tower Inland Observation Network (JR-STATION). We selected three sites in Western Siberia because they are deemed particularly effective for detecting CH₄ emissions from O&G facilities for two reasons: (1) the observation equipment is mounted on a tower situated along a gas pipeline, and (2) its location, over 200 km away from urban areas, minimizes interference from local human activities. To reduce the effects of CH₄ emissions from the Western Siberian wetlands and atmospheric convection, we utilized nighttime (20:00 to 04:00) data of winter season (January, February, November, and December). Our analysis found a linear correlation between the variabilities of atmospheric excess CH₄ and CO₂ (ΔCH₄ and ΔCO₂) influenced by atmospheric conditions (stability). We propose that high emission ratios (ΔCH₄/ΔCO₂) can be interpreted as signs of CH₄ leakage under the assumption of no interannual variations in biospheric CO₂ fluxes during the sub-zero winter season. The ΔCH₄/ΔCO₂ ratio has exhibited a decline across three observation sites situated several hundred kilometers apart from 2005 to 2021, indicating a reduction in CH₄ leakages from O&G facilities in Western Siberia and supporting the results from the BU estimates.