An Estimate of Natural Gas Methane Emissions from California Homes

Abstract

We estimate postmeter methane (CH) emissions from California's residential natural gas (NG) system using measurements and analysis from a sample of homes and appliances. Quiescent whole-house emissions (i.e., pipe leaks and pilot lights) were measured using a mass balance method in 75 California homes, while CH to CO emission ratios were measured for steady operation of individual combustion appliances and, separately, for transient operation of three tankless water heaters. Measured quiescent whole-house emissions are typically <1 g CH/day, though they exhibit long-tailed gamma distributions containing values >10 g CH/day. Most operating appliances yield undetectable CH to CO enhancements in steady operation (<0.01% of gas consumed), though storage water heaters and stovetops exhibit long-tailed gamma distributions containing high values (∼1-3% of gas consumed), and transients are observed for the tankless heaters. Extrapolating results to the state-level using Bayesian Markov chain Monte Carlo sampling combined with California housing statistics and gas use information suggests quiescent house leakage of 23.4 (13.7-45.6, at 95% confidence) Gg CH, with pilot lights contributing ∼30%. Emissions from steady operation of appliances and their pilots are 13.3 (6.6-37.1) Gg CH/yr, an order of magnitude larger than current inventory estimates, with transients likely increasing appliance emissions further. Together, emissions from residential NG are 35.7 (21.7-64.0) Gg CH/yr, equivalent to ∼15% of California's NG CH emissions, suggesting leak repair, improvement of combustion appliances, and adoption of nonfossil energy heating sources can help California meet its 2050 climate goals.

Majority of US urban natural gas emissions unaccounted for in inventories

“…In bottom-up studies of residential and commercial buildings, appliances and furnaces were reported to have loss rates of 0.1 to 0.3% of consumed gas (20,21,23); transmission (compressor stations, etc.) is estimated to have a loss rate of 0.2% (4).…”

Spatio‐temporally Resolved Methane Fluxes From the Los Angeles Megacity

“…The study also reaffirmed existing theories that a fraction of variability in enhancement and emissions in the basin is correlated with air temperature and energy demand. However, this has not been conclusively established in either this study or previous studies and would require detailed investigation, that is, studies that can isolate this process at the level of households (e.g., Fischer et al, 2018). Similarly, identification of the impact of episodic processes and apportioning of fluxes to specific facilities remained elusive due to the density and coverage provided by the current in situ network, indicating a requirement for a denser network, the establishment of which should be guided by pseudo data-inverse modeling studies that account for atmospheric transport (e.g., Pillai et al, 2012) in informing fluxes at an in situ site from near-and farfield sources.…”

“…However, this has not been conclusively established in either this study or previous studies and would require detailed investigation, that is, studies that can isolate this process at the level of households (e.g., Fischer et al, 2018). However, this has not been conclusively established in either this study or previous studies and would require detailed investigation, that is, studies that can isolate this process at the level of households (e.g., Fischer et al, 2018).…”

Atmospheric Methane Emissions Correlate With Natural Gas Consumption From Residential and Commercial Sectors in Los Angeles

“…There is increasing evidence that the probability density functions for CH 4 emissions have a long tail, characterized by a small number of emitters with very large emissions, perhaps due to malfunctioning equipment or improper operating conditions (Zavala-Araiza et al, 2015). This will require a concerted measurement campaign examining large numbers of emitters (thousands) under actual operating conditions targeting residential, commercial, and industrial sectors (Fischer et al, 2018).…”