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. 2025 May 27;59(20):9968-9979.
doi: 10.1021/acs.est.4c14090. Epub 2025 May 14.

An Unexpected Seasonal Cycle in U.S. Oil and Gas Methane Emissions

Lei Hu  1 , Arlyn E Andrews  1 , Stephen A Montzka  1 , Scot M Miller  2 , Lori Bruhwiler  1 , Youmi Oh  3 , Colm Sweeney  1 , John B Miller  1 , Kathryn McKain  1 , Sergio Ibarra Espinosa  3 , Kenneth Davis  4   5 , Natasha Miles  1   4 , Marikate Mountain  6 , Xin Lan  3 , Andy Crotwell  3 , Monica Madronich  3 , Thomas Mefford  3 , Sylvia Michel  7 , Sander Houwelling  8
Affiliations

An Unexpected Seasonal Cycle in U.S. Oil and Gas Methane Emissions

Lei Hu et al. Environ Sci Technol. .

Abstract

Accurate quantification of methane (CH4) emissions is essential for understanding changes in its atmospheric abundance. Atmospheric observations can supply independent emission information that complements and strengthens inventory-based estimates. In this study, we quantified annual and monthly U.S. CH4 emissions in 2008-2021 using inverse modeling of ground and airborne measurements at sites across the U.S. with 10-12 km atmospheric transport simulations. While the magnitude, spatial distribution, and trend of the estimated CH4 emissions align with some previous studies, our results reveal an unexpected seasonal cycle in CH4 emissions from the oil and gas sector, where wintertime emissions are about 40 (20-50, 2σ) % higher than summertime. This seasonality is supported by methane and propane measurements at these same sites, as well as methane isotope measurements made from an independent aircraft campaign over the U.S. Although the exact cause of this emission seasonality is unclear, its spatial distribution indicates that the enhanced CH4 emissions are primarily from natural gas production regions, and to a lesser extent, from natural gas consumption in winter.

Keywords: anthropogenic emissions; atmospheric observations; greenhouse gas; inverse modeling; seasonal variation; top-down estimates.

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Figures

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U.S. total net CH4 emissions derived from this study and from other inverse estimates. (a) Multi-year average annual CH4 emissions derived from this study and other studies. Errorbars indicate 2σ or the range reported by other studies. Note that some of the studies focused on a different time period from this study. The individual study periods are listed in Table S2. (b) Normalized multi-year average monthly CH4 emissions from this study (a black line with a gray shading denoting the 95% confidence interval), CT-CH4-2023 (red circles connected with a red line), and CAMS (green squares connected with a green line) between 2015 and 2017 and from Miller et al. (blue triangles connected with a blue line) for 2007–2008. (c) Trends in U.S. CH4 emissions derived from this study, CT-CH4-2023, and CAMS. Emissions are normalized by the average values in 2015–2017. Color shadings in panels (b,c) denote the 95% confidence interval.
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Seasonal variations of CH4 emissions derived for regions dominated by oil and gas production versus those dominated by wetlands and agriculture. (a) Normalized multi-year average seasonal cycle of CH4 from the central north (blue) and central south (red) regions of the U.S. between 2015 and 2017. (b) Definitions of central north (blue) and central south (red) regions. (c,d) Multi-year average annual emissions of CH4 in 2015–2017 and their associated 2σ uncertainties. (e,f) Areas with enhanced winter CH4 emissions (upper panel) and annual oil and gas CH4 emissions reported by Maasakkers et al. (2023) (lower panel). (g,h) Areas with enhanced summer CH4 emissions (upper panel) and annual CH4 emissions from wetland and manure management (lower panel). Wetland emissions are the average between the Kaplan and TEM models, whereas emissions from manure management are from Maasakkers et al. (2023). Grid cells with light blue dots indicate areas with wetland CH4 emissions, whereas grid cells with green crosses indicate areas with CH4 emissions from manure management. Panels (c–h) show emissions in nmol m–2 s–1.
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Synthetic-true, prior, posterior CH4 emissions from OSSEs. (a) Synthetic-true annual emissions averaged between 2015 and 2017. (b) Areas with enhanced winter emissions in the synthetic-true emissions. (c) Areas with enhanced summer emissions in the synthetic-true emissions. (d–f) The same as panels (a–c) but for prior emissions. (g–i) The same as panels (a–c) but for posterior emissions. (j–k) Multi-year average monthly emissions for CN and CS regions from synthetic-true emissions, prior, and posterior emissions between 2015 and 2017. The definitions of the CN and CS regions are shown in Figure .
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4
Seasonal cycle in U.S. C3H8 emissions and fossil fuel CH4 emissions estimated from atmospheric inversions of C3H8 or δ13CH4 observations. (a,b) Multi-year average annual and monthly C3H8 emissions between 2008 and 2015. (c) Areas with enhanced winter C3H8 emissions relative to summer. (d) Locations of δ13CH4 samples collected from ACT-America campaigns. (e) δ13CH4 source signatures derived from ACT-America campaigns. (f) Estimated U.S. fossil fuel and microbial CH4 emissions.
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