Lagrangian inversion of anthropogenic CO2 emissions from Beijing using differential column measurements

We estimated CO2 emissions from the Beijing region of China using differential ground-based observations of the column-averaged dry air mole fractions of CO2 ( Delta XCO2,obs; urban minus upwind background column observations) in winter (1 November 2020-1 March 2021). Beijing is one of the most world's populated cities and the CO2 emissions from this region contain large uncertainties in different bottom-up anthropogenic inventories. Differential measurements are potentially able to capture urban signals over Beijing (3.46 +/- 2.35 ppm). The simulated XCO2 enhancements were calculated ( Delta XCO2, sim) based on three emission inventories (the Open-source Data Inventory for Anthropogenic CO2 (ODIAC), Multiresolution Emission Inventory for China (MEIC) and Emissions Database for Global Atmospheric Research (EDGAR) datasets) for Beijing. The Delta XCO2,sim values based on the ODIAC dataset were much higher than the observations, whereas the values from the EDGAR dataset were much lower and the MEIC dataset was more consistent. We performed a Lagrangian inversion framework based on Bayesian theory. The average and uncertainty of a priori estimates (12.18 +/- 8.0, 7.09 +/- 7.5 and 3.53 +/- 11.4 mu mol (m(2) s)(-1)) were optimized to the posterior emissions (9.44 +/- 5.7, 7.13 +/- 4.9 and 7.15 +/- 5.7 mu mol (m(2) s)(-1)), suggesting that the three posterior estimates tended to converge to become more consistent, transport errors (especially the horizontal transport errors) and the spatially uneven corrections in Beijing were the main reason for the differences between the posterior estimates. Sensitivity tests suggested that the prescribed spatial and temporal structures affected up to about 12.9%, 4.9% and 20.8%, respectively, of the three inventories.