Controlled-release testing of the static chamber methodology for direct measurements of methane emissions

Abstract

Direct measurements of methane emissions at the component level provide the level of detail necessary for the development of actionable mitigation strategies. As such, there is a need to understand the magnitude of component-level methane emission sources and to test methane quantification methods that can capture methane emissions at the component level used in national inventories. The static chamber method is a direct measurement technique that has been applied to measure large and complex methane sources, such as oil and gas infrastructure. In this work, we compile methane emission factors from the Intergovernmental Panel on Climate Change (IPCC) Emission Factor Database in order to understand the magnitude of component-level methane flow rates, review the tested flow rates and measurement techniques from 40 controlled-release experiments, and perform 64 controlled-release tests of the static chamber methodology with mass flow rates of 1.02, 10.2, 102, and 512h-1 of methane. We vary the leak properties, chamber shapes, chamber sizes, and use of fans to evaluate how these factors affect the accuracy of the static chamber method. We find that 99% of the component-level methane emission rates from the IPCC Emission Factor Database are below 100h-1 and that 77% of the previously available controlled-release experiments did not test for methane mass flow rates below 100h-1. We also find that the static chamber method quantified methane flow rates with an overall accuracy of +14/-14% and that optimal chamber configurations (i.e., chamber shape, volume, and use of fans) can improve accuracy to below ±5%. We note that smaller chambers (≤20L) performed better than larger-volume chambers (≥20L), regardless of the chamber shape or use of fans. However, we found that the use of fans can substantially increase the accuracy of larger chambers, especially at higher methane mass flow rates (≥100h-1). Overall, our findings can be used to engineer static chamber systems for future direct measurement campaigns targeting a wide range of sources, including landfills, sewerage utility holes, and oil and natural gas infrastructure.