Methane Emissions from Postmeter Residential Natural Gas Infrastructure: Integrating Existing Data to Inform California’s Statewide Inventory

Abstract This study compiles, synthesizes and analyzes existing measurements of methane emissions from residential postmeter natural gas infrastructure, including (1) all infrastructure within a home under quiescent conditions, (2) pilot lights as discrete sources, (3) sustained combustion of main appliance burners, and (4) transient emissions during ignition and extinguishment. Quiescent leak measurements in 64 houses and emissions from 39 pilots and 509 appliances, mostly for cooking, water heating and space heating, are combined with usage estimates to calculate annual emissions by appliance, housing type, and statewide in California. Per appliance, tankless and storage water heaters have the highest annual emissions (mean estimates of 2456 and 395 g CH4 yr–1, respectively) and the average pilot emits 355 g CH4 yr–1. Statewide residential postmeter emissions are estimated at 32.1 (90% CI: 21.0–52.9) Gg CH4 yr–1, improving a prior estimate from the same quiescent data, 9 pilots and 129 appliances. This postmeter estimate is 2.2% of statewide methane emissions. This work also advances knowledge through improved estimates of pilot emissions, which account for 23% of quiescent and 15% of total residential; adding transients, estimated at 11% of total; and providing inventories by appliance category and process.