Methane emissions in the United States, Canada, and Mexico: Evaluation of national methane emission inventories and sectoral trends by inverse analysis of in situ (GLOBALVIEWplus CH<sub>4</sub> ObsPack) and satellite (GOSAT) atmospheric observations

Abstract

Abstract. We quantify methane emissions and their 2010–2017 trends by sector in the contiguous United States (CONUS), Canada, and Mexico by inverse analysis of in situ (GLOBALVIEWplus CH4 ObsPack) and satellite (GOSAT) atmospheric methane observations. The inversion uses as prior estimate the national anthropogenic emission inventories for the three countries reported by the US Environmental Protection Agency (EPA), Environment and Climate Change Canada (ECCC), and the Instituto Nacional de Ecologia y Cambio Climatico (INECC) in Mexico to the United Nations Framework Convention on Climate Change (UNFCCC), and thus serves as an evaluation of these inventories in terms of their magnitudes and trends. Emissions are optimized with a Gaussian mixture model (GMM) at 0.5° × 0.625° resolution and for individual years. Optimization is done analytically using log-normal error forms. This yields closed-form statistics of error estimates and information content on the posterior (optimized) estimates, allows better representation of the high tail of the emission distribution, and enables construction of a large ensemble of inverse solutions using different observations and assumptions. We find that GOSAT and in situ observations are largely consistent and complementary in the optimization of methane emissions for North America. Mean 2010–2017 anthropogenic emissions from our base GOSAT + in situ inversion, with ranges from the inversion ensemble, are 36.9 (32.5–37.8) Tg a−1 for CONUS, 5.3 (3.6–5.7) Tg a−1 for Canada, and 6.0 (4.7–6.1) Tg a−1 for Mexico. These are higher than the most recent reported national inventories of 26.0 Tg a−1 for the US (EPA), 4.0 Tg a−1 for Canada (ECCC), and 5.0 Tg a−1 for Mexico (INECC). The correction in all three countries is largely driven by a factor of 2 underestimate in emissions from the oil sector with major contributions from the south-central US, western Canada, and southeast Mexico. Total CONUS anthropogenic emissions in our inversion peak in 2014, in contrast to the EPA report of a steady decreasing trend over 2010–2017. This reflects combined effects of increases in emissions from the oil and landfill sectors, decrease from the gas, and flat emissions from the livestock and coal sectors. We find decreasing trends in Canadian and Mexican anthropogenic methane emissions over the 2010–2017 period, mainly driven by oil and gas emissions. Our best estimates of mean 2010–2017 wetland emissions are 8.4 (6.4–10.6) Tg a−1 for CONUS, 9.9 (7.8–12.0) Tg a−1 for Canada, and 0.6 (0.4–0.6) Tg a−1 for Mexico. Wetland emissions in CONUS show an increasing trend of 2.6 (1.7–3.8) % a−1 over 2010–2017 correlated with precipitation.

Integrated Methane Inversion (IMI 1.0): a user-friendly, cloud-based facility for inferring high-resolution methane emissions from TROPOMI satellite observations

“…It enables no-cost error analysis by producing an ensemble of solutions to explore the sensitivity to inversion parameters. The algorithm is fully documented in the literature Maasakkers et al, 2019Zhang et al, 2021;Lu et al, 2022), including applications to TROPOMI data (Zhang et al, 2020;Qu et al, 2021;Shen et al, 2021Shen et al, , 2022Z. Chen et al, 2022).…”

“…It requires explicit construction of the Jacobian matrix expressing the sensitivity of concentrations to emissions, but this is readily done on supercomputing clusters as an embarrassingly parallel problem (Maasakkers et al, 2019). Two major advantages of the analytical solution are that (1) it provides closed-form characterizations of the posterior error pdf and the information content of the observations, and (2) it allows easy generation of solution ensembles exploring the inversion parameter space (Lu et al, 2022).…”

Quantifying methane emissions from the global scale down to point sources using satellite observations of atmospheric methane

“…Global observation of methane from space began with the SCIAMACHY instrument (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)30 × 60 km 2 pixels) (Frankenberg et al, 2005) and has continued since with the TANSO-FTS instrument aboard GOSAT (2009-present, 10 km circular pixels separated by about 270 km; Parker et al, 2020) and the TROPOMI instrument (2018-present, 5.5 × 7 km 2 pixels; Lorente et al, 2021a). Many studies have used these satellite observations to quantify methane emissions globally (Bergamaschi et al, 2013;Alexe et al, 2015;Wang et al, 2019;Qu et al, 2021), on continental scales (Wecht et al, 2014;Lu et al, 2022), on finer regional scales (Miller et al, 2019;Zhang et al, 2020;, and for large point sources (Pandey et al, 2019;Sadavarte et al, 2021;Maasakkers et al, 2022a, b). Targeted observation of methane point sources from space began with the 2015 Aliso Canyon blowout using the Hyperion hyperspectral sensor (Thompson et al, 2016) and has since continued with the GHGSat instruments (2016-present, 25 × 25 m 2 pixels; Jervis et al, 2021).…”

Satellite quantification of oil and natural gas methane emissions in the US and Canada including contributions from individual basins

“…This is offset by fast growing emissions in the Permian, where the O/G production Our top-down estimate in Canada is 2.2 ± 0.6 (±2σ) Tg a -1 , which is 40% higher than the most recent ECCC reported emissions (ECCC, 2020) and EDGAR v6 (Crippa et al, 2020) in 2018, and is at the lower end of other top-down studies (2.3-3.6 Tg a -1 ) for 2010-2017 (Lu et al, 2021b;Baray et al, 2021;Maasakkers et al, 2021;Chan et al, 2020). This could be due to a decreasing trend of O/G emissions after 2014 in Canada, as reported by both the bottom-up national inventory (ECCC, 2020) and inversion studies (Lu et al, 2021b), and reflecting the ongoing regulations efforts following Canada's commitment to reduce O/G methane emissions by 40-45% by 2025 relative to the 2012 level (ECCC, 2017). When normalized by annual natural gas production (7.1x10 6 MMcf, UNFCC https://unfccc.int/documents/271492; assuming the average CH4 content is 90%) in 2019, the national O/G mean leakage rate is 1.7% in Canada.…”

“…for 2018,Alvarez et al (2018) for 2015,Maasakkers et al (2021) for 2010-2015,Lu et al (2021b, ECCC (2020 for 2018 (used as prior estimate for our work),Baray et al (2021) for 2010-2015, and 575Chan et al (2020) for 2010-2017 Maasakkers et al (2021). andLu et al (2021b) did not include the O/G emissions in Alaska so we add 0.1 Tg a -1 of emissions(EPA, 2020;Maasakkers et al, 2016) here to obtain the US national total.National estimates of oil/gas methane emissions Author (years of emissions) Methane emissions from 14 oil and natural gas production basins in the US. Estimates from field campaigns are compared to the gridded EPA and ECCC inventories for the US and Canada (left panel) and to results from our TROPOMI inversion using these inventories as prior estimates (right panel).…”