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We apply a continental-scale inverse modeling system for North America basedon the GEOS-Chem model to optimize California methane emissions at1/2° × 2/3° horizontal resolution using atmospheric observationsfrom the CalNex aircraft campaign (May–June 2010) and from satellites.Inversion of the CalNex data yields a best estimate for total Californiamethane emissions of 2.86 ± 0.21 Tg a−1, compared with 1.92 Tg a−1in the EDGAR v4.2 emission inventory used as a priori and 1.51 Tg a−1 in theCalifornia Air Resources Board (CARB) inventory used forstate regulations of greenhouse gas emissions. These results are consistentwith a previous Lagrangian inversion of the CalNex data. Our inversionprovides 12 independent pieces of information to constrain the geographicaldistribution of emissions within California. Attribution to individualsource types indicates dominant contributions to emissions fromlandfills/wastewater (1.1 Tg a−1), livestock (0.87 Tg a−1), andgas/oil (0.64 Tg a−1). EDGAR v4.2 underestimates emissions fromlivestock, while CARB underestimates emissions from landfills/wastewater andgas/oil. Current satellite observations from GOSAT can constrain methaneemissions in the Los Angeles Basin but are too sparse to constrain emissionsquantitatively elsewhere in California (they can still be qualitativelyuseful to diagnose inventory biases). Los Angeles Basin emissions derivedfrom CalNex and GOSAT inversions are 0.42 ± 0.08 and0.31 ± 0.08 Tg a−1that the future TROPOMI satellite instrument (2015 launch) will be able toconstrain California methane emissions at a detail comparable to the CalNexaircraft campaign. Geostationary satellite observations offer even greaterpotential for constraining methane emissions in the future

atmospheric chemistry and physics

Spatially resolving methane emissions in California: constraints from the CalNex aircraft campaign and from present (GOSAT, TES) and future (TROPOMI, geostationary) satellite observations