Using Multiscale Ethane/Methane Observations to Attribute Coal Mine Vent Emissions in the San Juan Basin From 2013 to 2021

• Published in: Journal of geophysical research. Atmospheres 2022-09, Vol.127 (18), p.n/a
• Main Authors: Meyer, Aaron G., Lindenmaier, Rodica, Heerah, Sajjan, Benedict, Katherine B., Kort, Eric A., Peischl, Jeff, Dubey, Manvendra K.
• Format: Article
• Language: English
• Subjects: Air pollution; Airborne remote sensing; Airborne sensing; Anthropogenic factors; Coal; Coal mines; Coal mining; Earth sciences; Emission measurements; Emissions; Empirical analysis; ENVIRONMENTAL SCIENCES; Ethane; Fossil fuels; Geophysics; Greenhouse gases; Heterogeneity; Hydrocarbons; In situ measurement; Instruments; Inversions; Measurement; Measurement methods; Measurement techniques; Measuring instruments; Methane; Mixing ratio; multiscale; Natural gas; Pollutants; ratio; Ratios; Remote sensing; source apportionment
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2022JD037092

Source attribution of natural gas emissions from fossil fuels in New Mexico's San Juan Basin (SJB) is challenging due to source heterogeneity and emissions transience. We demonstrate that ethane (C2H6) to methane (CH4) mixing ratios can identify and separate sources over different scales using various measurement techniques. We report simultaneous CH4 and C2H6 observations near a coal mine vent and oil and gas (O&G) emission sources using ground‐based in situ measurements in 2020/2021. During these campaigns, we observed a stable coal vent C2H6:CH4 ratio of 1.28% ± 0.11%, discernibly different than nearby O&G source ratios ranging from 0.9% to 16.8%. We analyze airborne observations of the SJB taken in 2014/2015 that exhibit similar coal vent ratios and further show the region's heterogeneity. We identify episodic O&G sources, including a gas plant source detected in 2014/2015 that is absent in our 2020/2021 data. We examine total column observations of C2H6 and CH4 made in 2013 with a solar spectrometer and find a C2H6:CH4 ratio of 1.3% ± 0.4% for the coal vent. The stable and unique coal vent ratio relative to other O&G sources in the region is used to demonstrate that consistent attribution is possible using various measurement methods at multiple scales across many years. Finally, we demonstrate that using C2H6 as a proxy for fossil CH4 inversions can inform detailed basin‐scale inversions, provided we understand source specific changes in the C2H6:CH4 ratio like we report in the SJB. Plain Language Summary Oil, gas, and coal production processes are known to emit methane, a potent greenhouse gas, and other hydrocarbon air pollutants. Attributing these emissions to specific anthropogenic fossil sources is challenging in the vast and variable infrastructure. Ethane is often co‐emitted with methane and the ratio of ethane to methane in emission sources varies significantly with source types. By measuring this ratio with high sensitivity and accuracy, we can “fingerprint” gas sources by their unique ratio. We report simultaneous measurements of ethane and methane, and an empirical analysis of the ratio to demonstrate source specific attribution. Our varied measurement techniques spanning spatial scales (near‐source ground, airborne, and remote sensing) were used to sample sources in New Mexico's San Juan basin over 8 years. Despite a diverse and changing emissions environment, ethane to methane ratios were successfully used to identify and apportion sever