Residential natural gas meter set assemblies (MSAs) emit methane (CH), but reported emissions factors vary. To test existing emissions factors, we quantified CH emissions from 37 residential MSAs in Calgary, Alberta, Canada. A notable difference with previous studies is the targeted measurement of regulator vents in this study, which were measured with a static chamber, while fugitives were measured with a modified hi-flow sampler. Emissions were dominated by pressure regulator vents (emissions factor = 1.18 g CH/h/MSA), but 7 fugitives were found (emissions factor = 0.018 g CH/h/MSA). Six regulator vents were emitting at notably higher rates (≥ 1.79 g CH/h/MSA). The total empirical emissions factor was 1.20 g CH/h/MSA (95 % CI, 1.03 to 1.37 g/h/MSA). This is ∼7 times higher than the emissions factor for residential MSAs used in the U.S. EPA's Greenhouse Gas Inventory, which may not include emissions from regulator vents. Upscaling to annual CH emissions in Calgary indicates 3234.6 t CH/yr (95 % CI, 2776.4 t to 3692.9 t CH/yr) could be emitted from MSAs. This is equivalent to 4.1 % (95 % CI, 3.5 % to 4.7 %) of total city-level CH emissions as estimated with satellite data. Results suggest residential MSA emissions may be under-estimated and further study isolating root causes of regulator vent emissions is required to guide mitigation and improve emissions modeling.
