Reconciling Regional Mass Balance and Point Source Measurements for Understanding Methane Emissions in the Appalachian Basin

Anthropogenic sources of methane, especially those from the oil and gas industry, are significant. Increasingly, global measurement campaigns have been conducted to capture regional emissions intensity using satellite and mass balance technologies. However, these technologies often lack the fine-scale resolution needed for detailed source attribution, making them difficult to use for mitigation prioritization. Meanwhile, individual operators are employing aerial technologies to measure their assets and assist in leak detection and repair initiatives, but this fine-scale data is not used to inform the regional estimates. This study focuses on reconciling aircraft-based regional mass balance data with aircraft-based point source measurements in identical regions of the Appalachian Basin of the United States in 2024. Aerial LIDAR measurements were used to measure approximately 6000 sites, including all major oil and gas and non-oil and gas sources. Regional mass balance flights were conducted on subdivided polygons encompassing the sites surveyed by the aerial LIDAR measurements. Some emission sources have been deliberately excluded due to cost, such as pipelines, distribution systems and non-producing wells. Comparing the sum of the point sources measured and the mass balance approaches will allow us to examine the relevance of the sources that were not measured. Additionally, while the mass balance measurements and point source measurements occur in the same quarter, the flights are not contemporaneous. It is well documented that emissions from oil and gas sources vary in their size and duration, with large emission events that may be short in duration. This can lead to considerable disagreement between the point source measurements and the regional mass balance estimates. This work will address the short duration, large emission events and their effect on the uncertainty in the regional methane emission estimates.