A Method for Estimating the Background Column Concentration of CO₂ Using the Lagrangian Approach

With the rapid growth of greenhouse gas (GHG) monitoring satellites, more and more studies focused on the issue of inversion/optimization of carbon dioxide (CO ₂ ) fluxes using satellite-derived XCO ₂ observations in recent years. A common and critical challenge in this framework is the separation of background and anomalies from XCO ₂ observations, which directly affect the performance of the CO ₂ fluxes’ inversion. We proposed a novel method to accurately extract background XCO ₂ from satellite observations. A series of observing system simulation experiments (OSSEs) were performed to test the performance of the method. We found that the bias and uncertainty of the background concentration are below 0.01 and 0.05 ppm in the given cases, respectively. Based on this method, we selected five overpasses from 2014 to 2016 to demonstrate a regional-scale flux inversion near Riyadh. The comparison with the two previous methods shows that the posterior simulated XCO ₂ by the method proposed in this article can match better with the observed XCO ₂ from Orbiting Carbon Observatory-2 (OCO-2).