CO2 Emissions Estimate From Mexico City Using Ground- and Space-Based Remote Sensing

The Mexico City Metropolitan Area (MCMA) stands as one of the most densely populated urban regions globally. To quantify the urban ${\text{CO}}_2$ emissions in the MCMA, we independently assimilated observations from a dense column-integrated Fourier transform infrared (FTIR) network and OCO-3 Snapshot Area Map observations between October 2020 and May 2021. Applying a computationally efficient analytical Bayesian inversion technique, we inverted for surface fluxes at high spatio-temporal resolutions (1-km and 1-hr). The fossil fuel (FF) emission estimates of 5.08 and 6.77 Gg${\text{CO}}_2$/hr reported by the global and local emission inventories were optimized to 4.85 and 5.51 Gg${\text{CO}}_2$/hr based on FTIR observations over this 7 month period, highlighting a convergence of posterior estimates. The modeled biogenic flux estimate of −0.14 Gg${\text{CO}}_2$/hr was improved to −0.33 to −0.27 Gg${\text{CO}}_2$/hr, respectively. It is worth noting that utilizing observations from three primary sites significantly enhanced the accuracy of estimates (13.6 $\sim$ 29.2%) around the other four. Using FTIR posterior estimates can improve simulation with the OCO-3 data set. OCO-3 shows a similar decreasing trend in FF emissions (from 6.37 Gg${\text{CO}}_2$/hr to 6.36 and 5.04 Gg${\text{CO}}_2$/hr) as FTIR, but its correction trends for biogenic sources differ, changing from 0.37 to 0.48 Gg${\text{CO}}_2$/hr. The primary reason is OCO-3's lower temporal sampling density. Aligning the FTIR inversion timing with that of OCO-3 yielded comparable corrections for FF emissions, yet discrepancies in biogenic emissions persisted, which can be attributed to their different sampling locations in the rural region and discrepancy in X${\text{CO}}_2$ observations. Our findings mark a significant step toward validating OCO-3 and FTIR inversion results in metropolitan region.