Characterizing point-source carbon emissions by combining TROPOMI CO and OCO CO2 data.

Understanding and independently validating carbon emissions from concentrated point sources is vital to support climate policy. Satellite-based quantifications of CO2 point source emissions have been limited by the spatial coverage of current satellite instruments. We combine three different satellite instruments to determine carbon monoxide (CO) and carbon dioxide (CO2) emissions of seven large cities and six industrial complexes. We first estimate CO emission rates using TROPOMI CO observations with the Cross-Sectional Flux method. Subsequently, CO2 emission rates are calculated by multiplying with the ratio of TROPOMI-observed CO enhancements and CO2 enhancements from OCO-2 and OCO-3, also representing the combustion efficiency. We use synthetic observations to validate our approach and show that the inclusion of TROPOMI CO observations increases the number of possible CO2 emission quantifications. Using 2018-2023 observations, we find lower CO emission rates for Delhi and Lahore than the EDGAR emission inventory. In contrast, our CO emission estimates exceed bottom-up inventory estimates for most industrial sources. This is caused by observed combustion efficiencies that are generally lower than those reported in emission inventories. Our CO2 emission estimates show better agreement with EDGAR than the CO emissions, especially for industrial sources. We find higher CO2 emission rates than EDGAR for the cities of Delhi, Lahore, and Cairo that better agree with the ODIAC inventory. Our work shows the importance of CO as a co-emitted species, and paves the way for a similar approach to be applied to the combination of TROPOMI, its successor Sentinel-5, and the future CO2M satellites.