Assessing the Methane Emissions from Natural Gas-Fired Power Plants and Oil Refineries

Presently, there is high uncertainty in estimates of methane (CH₄) emissions from natural gas-fired power plants (NGPP) and oil refineries, two major end users of natural gas. Therefore, we measured CH₄ and CO₂ emissions at three NGPPs and three refineries using an aircraft-based mass balance technique. Average CH₄ emission rates (NGPPs: 140 ± 70 kg/h; refineries: 580 ± 220 kg/h, 95% CL) were larger than facility-reported estimates by factors of 21–120 (NGPPs) and 11–90 (refineries). At NGPPs, the percentage of unburned CH₄ emitted from stacks (0.01–0.14%) was much lower than respective facility-scale losses (0.10–0.42%), and CH₄ emissions from both NGPPs and refineries were more strongly correlated with enhanced H₂O concentrations (<i>R</i>²_avg = 0.65) than with CO₂ (<i>R</i>²_avg = 0.21), suggesting noncombustion-related equipment as potential CH₄ sources. Additionally, calculated throughput-based emission factors (EF) derived from the NGPP measurements made in this study were, on average, a factor of 4.4 (stacks) and 42 (facility-scale) larger than industry-used EFs. Subsequently, throughput-based EFs for both the NGPPs and refineries were used to estimate total U.S. emissions from these facility-types. Results indicate that NGPPs and oil refineries may be large sources of CH₄ emissions and could contribute significantly (0.61 ± 0.18 Tg CH₄/yr, 95% CL) to U.S. emissions

Aircraft-Based Measurements of Point Source Methane Emissions in the Barnett Shale Basin

We report measurements of methane (CH₄) emission rates observed at eight different high-emitting point sources in the Barnett Shale, Texas, using aircraft-based methods performed as part of the Barnett Coordinated Campaign. We quantified CH₄ emission rates from four gas processing plants, one compressor station, and three landfills during five flights conducted in October 2013. Results are compared to other aircraft- and surface-based measurements of the same facilities, and to estimates based on a national study of gathering and processing facilities emissions and 2013 annual average emissions reported to the U.S. EPA Greenhouse Gas Reporting Program (GHGRP). For the eight sources, CH₄ emission measurements from the aircraft-based mass balance approach were a factor of 3.2–5.8 greater than the GHGRP-based estimates. Summed emissions totaled 7022 ± 2000 kg hr^–1, roughly 9% of the entire basin-wide CH₄ emissions estimated from regional mass balance flights during the campaign. Emission measurements from five natural gas management facilities were 1.2–4.6 times larger than emissions based on the national study. Results from this study were used to represent “super-emitters” in a newly formulated Barnett Shale Inventory, demonstrating the importance of targeted sampling of “super-emitters” that may be missed by random sampling of a subset of the total