Identification of natural gas leak sources using ethane/methane ratios and methane isotopic signatures

Abstract

Methane (CH₄) is the second largest greenhouse gases in the atmosphere. Its global anthropogenic emissions are equivalent to about 20% of total GHG emissions in CO₂-equivalent terms. Source identification for atmospheric CH₄, however, is not straight forward. This study conducted mobile measurements of CH₄, C₂H₆, CO₂, CO and stable CH₄ carbon isotope composition (δ¹³C-CH₄) at three natural gas compressor stations in China to obtain source signatures for ΔC₂H₆/ΔCH₄ (C₂:C₁) and δ¹³C-CH₄. The two northern stations showed consistent ΔC₂H₆/ΔCH₄ ratios (0.059 and 0.056) and δ¹³C-CH₄ values (−40.59 ‰ and −40.93 ‰), while the southern station exhibited a lower ratio (0.022) and less ¹³C-depleted δ¹³C-CH₄ values (−39.34 ‰), indicating different gas supply sources. Using these signatures, mobile surveys in adjacent urban and suburban areas identified 17 and 9 CH₄ emission sources near the northern and southern stations, respectively, with 58.9% and 66.7% attributed to natural gas leaks. On-road leak magnitudes spanned 0.77-101.69 L/min around Station #1 and 0.38-26.78 L/min around Station #3. In both regions, detections were dominated by small leaks (<4 L/min), including cases with multiple plume peaks evaluated individually. These findings highlight the effectiveness and practical importance of a dual-tracer approach for mobile platforms to reliably identify and quantify natural-gas-related CH₄ sources along road networks.