Majority of US urban natural gas emissions unaccounted for in inventories

Abstract

Across many cities, estimates of methane emissions from natural gas (NG) distribution and end use based on atmospheric measurements have generally been more than double bottom-up estimates. We present a top-down study of NG methane emissions from the Boston urban region spanning 8 y (2012 to 2020) to assess total emissions, their seasonality, and trends. We used methane and ethane observations from five sites in and around Boston, combined with a high-resolution transport model, to calculate methane emissions of 76 ± 18 Gg/yr, with 49 ± 9 Gg/yr attributed to NG losses. We found no significant trend in the NG loss rate over 8 y, despite efforts from the city and state to increase the rate of repairing NG pipeline leaks. We estimate that 2.5 ± 0.5% of the gas entering the urban region is lost, approximately three times higher than bottom-up estimates. We saw a strong correlation between top-down NG emissions and NG consumed on a seasonal basis. This suggests that consumption-driven losses, such as in transmission or end-use, may be a large component of emissions that is missing from inventories, and require future policy action. We also compared top-down NG emission estimates from six US cities, all of which indicate significant missing sources in bottom-up inventories. Across these cities, we estimate NG losses from distribution and end use amount to 20 to 36% of all losses from the US NG supply chain, with a total loss rate of 3.3 to 4.7% of NG from well pad to urban consumer, notably larger than the current Environmental Protection Agency estimate of 1.4% [R. A. Alvarez et al., Science 361, 186–188 (2018)].

Carbon and energy cost impacts of electrification of space heating with heat pumps in the US

“…In fact, due to increased radiative forcing of CH4 gas, Alvarez et al [33] estimate that emissions across the supply chain, per unit of gas consumed, results in roughly the same radiative forcing as does the combustion of delivered natural gas over a 20-year time horizon (+31% over 100 years). In addition, these CH4 leakage estimates do not include leaks in the local distribution systems or at end-uses (e.g., in buildings), which others have estimated to exceed the 2-3% figure for the larger distribution system [35]- [38]. If the impacts of CH4 and refrigerant leaks were included, both types of heating appliances would have increased carbon emissions.…”

Home is Where the Pipeline Ends: Characterization of Volatile Organic Compounds Present in Natural Gas at the Point of the Residential End User

“…Additionally, NG leak detection would be mediated by other factors as well, such as the location of a leak within a home, considering that the heavier sulfur-odorant compounds tend to sink versus CH 4 , which is lighter than air. Nonetheless, Sargent et al 22 recently found that an estimated 2.5 ± 0.5% of NG entering the Boston region is lost, noting that emissions are correlated with seasonal end use consumption implying that emissions may predominate from consumption-driven source types that includes beyond-the-meter leaks and residential end use appliances. The odorant content observed in end use NG in combination with known odor detection thresholds supports this hypothesis in the sense that small NG leaks may persist undetected and, therefore, may be more prevalent and not be immediately mitigated as has been previously assumed.…”

“…Downstream NG system loss estimates indicate that NG-sourced BTEX emissions contribute to a modest NMVOC enhancement that is currently not accounted for in emissions inventories. Using NG CH 4 leak estimates from McKain et al, 17 Plant et al, 20 and Sargent et al, 22 an estimated 338–608 kg/yr (745–1340 lbs/yr) of total BTEX is annually emitted alongside CH 4 leakage throughout Greater Boston. For context, 216 kg/yr (476 lbs/yr) of benzene emitted annually (estimated via NG methane emissions from 17 equates to nearly 10% of on-road diesel light-duty vehicles for all of Massachusetts).…”

Comparing national greenhouse gas budgets reported in UNFCCC inventories against atmospheric inversions

“…This different trend between inversions and the US NGHGIs might be attributed to CH 4 leakage from unconventional oil and gas extraction that may not be fully accounted for in NGHGIs (Allen, 2016). This type of oil and gas production became important after the mid-2000s and has emission factors that are twice larger than current values from the US Environmental Protection Agency (EPA) currently used in the NGHGIs, as shown by local and regional measurement campaigns (Alvarez et al, 2018;Sargent et al, 2021).…”