Quantification and evaluation of carbon monoxide emissions for high-emitting point sources using earth observation and bottom-up estimates

Carbon monoxide (CO) is an important air pollutant and precursor of ozone, plays an important role in atmospheric chemistry. Large quantities of carbon monoxide are emitted in coal-fired iron and steel  production processes, causing iron and steel plants to be the globally highest emitting point sources of CO. From the CORSO bottom-up global point source dataset, we select iron and steel plants thought to emit over 100 kt CO per year in 2021. For these plants, we obtain satellite-based emission estimates of carbon monoxide, applying the Cross-Sectional-Flux (CSF) method to TROPOMI for the period 2019-2021. We retain a global set of iron and steel plant yearly emission estimates of CO with satellite quantifications of 100 kt.yr^-1 and up. Previous research on European iron and steel plants  showed good agreement between bottom-up inventories, resource-intensive inversions and the low-cost CSF method. When we apply the CSF method outside of Europe we find substantial discrepancies between the bottom-up and top-down estimates, with large variations between regions. We examine potential sources of satellite under- or overestimation of the bottom-up inventory.