Improving Consistency in Methane Emission Quantification from the Natural Gas Distribution System across Measurement Devices

Efficient and cost-effective mitigation of methane emissions from local gas distribution systems requires full characterization of leaks across an urban region. Mobile real-time measurements of ambient CH4 provide a fast and effective approach to identify and quantify methane leaks. The objective of such methodologies is to relate emission rates to parameters obtained during mobile measurements. These parameters encompass the maximum methane enhancement detected while crossing a methane plume and the integrated area of the associated peak. The maximum enhancement is currently used for emission quantification in mobile measurements, but was suggested to exhibit inconsistency among various measurement devices. Based on controlled release experiments conducted in four cities (London, Toronto, Rotterdam, and Utrecht), emission estimation methodologies were evaluated. Integrated plume area was found to be a more robust metric across different methane gas analyzer devices than the maximum methane enhancement. A statistical function based on integrated plume area is proposed for more consistent emission estimations when using different instruments. Nevertheless, large temporal variations in CH4 concentration enhancements were observed for the same release rate in line with previous experiments. Evaluation of repeated measurements to address this uncertainty and enable differentiation among various leak sizes was included. This study recommends a minimum of three repeated measurements and an optimal range of 5-7 plume transects for effective emission quantification to prioritize repair actions.