Global atmospheric carbon monoxide budget 2000-2017 inferred from multi-species atmospheric inversions

We identify a declining trend in the global CO budget since 2000 (three inversions are broadly consistent during overlapping periods), driven by reduced anthropogenic emissions in the US and Europe (both likely from the transport sector), and in China (likely from industry and residential sectors), as well as by reduced biomass burning emissions globally, especially in equatorial Africa (associated with reduced burned areas).

We show that the trends and drivers of the inversion-based CO budget are not affected by the inter-annual variation assumed for prior CO fluxes. All three inversions contradict the global bottom-up inventories in the world's top two emitters: for the sign of anthropogenic emission trends in China (e.g., here 0.8 +/- 0.5% yr(-1) since 2000, while the prior gives 1.3 +/- 0.4% yr(-1)) and for the rate of anthropogenic emission increase in South Asia (e.g., here 1.0 +/- 0.6% yr(-1) since 2000, smaller than 3.5 +/- 0.4% yr(-1) in the prior inventory).

The posterior model CO concentrations and trends agree well with independent ground-based observations and correct the prior model bias. The comparison of the three inversions with different observation constraints further suggests that the most complete constrained inversion that assimilates CO, HCHO, and CH4 has a good representation of the global CO budget, and therefore matches best with independent observations, while the inversion only assimilating CO tends to underestimate both the decrease in anthropogenic CO emissions and the increase in the CO chemical production.