Characterizing anthropogenic methane sources in the Houston and Barnett Shale areas of Texas using the isotopic signature δC in CH.

Methane (CH) is an important greenhouse gas with its mixing ratio increasing in the global atmosphere. Identifying fingerprints of CH emissions is critical to understanding potential impacts of various anthropogenic sources in the Greater Houston area (GHA) and extensive natural gas operations in the Barnett Shale area (BSA) of Texas. Stable carbon isotope ratios of CH (δC) has been proposed to be a useful technique for differentiating individual CH sources. Measurements of CH mixing ratios and δC were sampled using a mobile laboratory equipped with cavity ring-down spectrometers (CRDS). Areal CH distributions and the background δC signature were obtained from filtered ambient signals; -47.0‰ (GHA) and - 48.5‰ (BSA) were calculated. The fingerprint of thirty-three anthropogenic sources in the two study areas were sampled with forty-four δC analyses conducted. Repeated measurements indicated the natural variation of δC signatures of individual CH sources. An unexpected massive CH fugitive leak was detected near the San Jacinto River Fleet site in Houston exhibiting an δC value around -42‰. Our results and findings demonstrate the utility of δCfor facilitating emission inventories and atmospheric modeling.