This study compares recent CO, NO, NMVOC, SO, BC and OC anthropogenic emissions from several state-of-the-art top-down estimates to global and regional bottom-up inventories and projections from five SSPs in several regions. Results show that top-down emissions exhibit similar uncertainty as bottom-up inventories in most regions, and even less in some such as China. In general, for all species the largest discrepancies are found outside of regions such as the U.S., Europe and Japan where the most accurate and detailed information on emissions is available. In some regions such as China, which has undergone dynamical economic growth and changes in air quality regulations during the last several years, the top-down estimates better capture recent emission trends than global bottom-up inventories. These results show the potential of top-down estimates to complement bottom-up inventories and to aide in the development of emission scenarios, particularly in regions where global inventories lack the necessary up-to-date and accurate information regarding regional activity data and emission factors such as Africa and India. Areas of future work aimed at quantifying and reducing uncertainty are also highlighted. A regional comparison of recent CO and NO trends in the five SSPs indicate that SSP126, a strong-pollution control scenario, best represents the trends from the from top-down and regional bottom-up inventories in the U.S., Europe and China, while SSP460, a low-pollution control scenario, lies closest to actual trends in West Africa. This analysis can be a useful guide for air quality forecasting and near-future pollution control/mitigation policy studies.
