2010-2015 North American methane emissions, sectoral contributions, and trends: a high-resolution inversion of GOSAT satellite observations of atmospheric methane.

We use 2010-2015 GOSAT satellite observations of atmospheric methane columns over North America in a high-resolution inversion of methane emissions, including contributions from different sectors and long-term trends. The inversion involves analytical solution to the Bayesian optimization problem for a Gaussian mixture model (GMM) of the emission field with up to 0.5° x 0.625° resolution in concentrated source regions. Analytical solution provides a closed-form characterization of the information content from the inversion and facilitates the construction of a large ensemble of solutions exploring the effect of different uncertainties and assumptions. Prior estimates for the inversion include a gridded version of the EPA Inventory of U.S. Greenhouse Gas Emissions and Sinks (GHGI) and the WetCHARTS model ensemble for wetlands. Our best estimate for mean 2010-2015 US anthropogenic emissions is 30.6 (range: 29.4-31.3) Tg a^-1, slightly higher than the gridded EPA inventory (28.7 (26.4-36.2) Tg a^-1). The main discrepancy is for the oil and gas production sectors where we find higher emissions than the GHGI by 35 % and 22 % respectively. The most recent version of the EPA GHGI revises downward its estimate of emissions from oil production and we find that these are a factor 2 lower than our estimate. Our best estimate of US wetland emissions is 10.2 (5.6-11.1) Tg a^-1, on the low end of the prior WetCHARTS inventory uncertainty range (14.2 (3.3-32.4) Tg a^-1) and calling for better understanding of these emissions. We find an increasing trend in US anthropogenic emissions over 2010-2015 of 0.4 % a^-1, lower than previous GOSAT-based estimates but opposite to the decrease reported by the EPA GHGI. Most of this increase appears driven by unconventional oil/gas production in the eastern US. We also find that oil/gas production emissions in Mexico are higher than in the nationally reported inventory, though there is evidence for a 2010-2015 decrease in emissions from offshore oil production. [ABSTRACT FROM AUTHOR]