Revisiting Methane Emissions from the Southwest Marcellus Shale Based on Airborne and Mobile Measurements

Natural gas production in the United States has increased rapidly over the past two decades, along with concerns of fugitive emissions of methane (CH₄) and its climate impacts. Quantification of CH₄ emissions from oil and gas operations is important for establishing scientifically sound policies for mitigating greenhouse gases. Aircraft mass balance experiments were conducted in 2015 and estimated CH₄ emissions from the O&G operations in the southwestern Marcellus Shale in PA and WV to be 21.2 kg/s for a ~4,200 km² study area. This accounts for ~1.1% of total natural gas production in this area, suggesting that for a 20‐year time scale, energy derived from the combustion of natural gas extracted from this region likely exerts a net climate benefit compared to coal. Since 2015, natural gas production from this area has increased by ~70%. The question is: has the CH₄ emission rate from this area changed from 2015 to 2023? We revisited this area recently with a research aircraft and a mobile lab equipped with additional measurements of chemical species and meteorological parameters, including ethane with a mid-IR absorption analyzer and 2-D wind fields with a differential GPS. Continuous measurements of ethane and CH₄ were made both in the air and on the ground and are compared to each other. Enhanced ethane-to-CH₄ ratios from the aircraft and mobile lab are used to characterize CH₄ emissions sources (i.e., from coal mines versus from O&G operations) in the area. CH₄ emissions from this area are estimated based on aircraft and mobile measurements and are compared with previous studies. Reasons and implications of methane emission changes from 2015 to 2023 are discussed.