OMI-Derived Mass- and Number-Conserved Estimation of Black Carbon Emissions

Black carbon (BC) emission estimates remain highly uncertain, especially in regions impacted by biomass burning (BB) and rapid urban expansion, where emissions are temporally variable and often misrepresented in bottom-up inventories(Liu, J.; Cohen, J. B.; He, Q.; Tiwari, P.; Qin, J. Accounting for NOx Emissions from Biomass Burning and Urbanization Doubles Existing Inventories over South, Southeast and East Asia. Commun. Earth Environ. 2024, 5 (1), 1−16. Lu, L.; Cohen, J. B.; Qin, K.; Li, X.; He, Q. Identifying Missing Sources and Reducing NOx Emissions Uncertainty over China Using Daily Satellite Data and a Mass-Conserving Method. Atmos. Chem. Phys. 2025, 25 (4), 2291−2309. Tiwari, P.; Cohen, J. B.; Lu, L.; Wang, S.; Li, X.; Guan, L.; Liu, Z.; Li, Z.; Qin, K. Multi-platform observations and constraints reveal overlooked urban sources of black carbon in Xuzhou and Dhaka. Commun. Earth Environ. 2025, 6 (1), 1−20.). This study introduces a novel top-down approach using the OMI-derived column densities of BC mass and number to estimate emissions via mass- and number-conservative methods. The analysis spans all of 2016 across South, Southeast, and East Asia, with particular focus on February to May─months marked by intensified BB and urban pollution events using an unbiased technique(Hawkins, L. R.; Abatzoglu, J. T.; Li, S.; Rupp, D. E. Anthropogenic Influence on Recent Severe Autumn Fire Weather in 414 the West Coast of the United States. Geophys. Res. Lett. 2022, 49 (4), e2021GL095496. Jain, P., Drivers and Impacts of the Record-Breaking 2023 Wildfire Season in Canada. Nat. Commun. 2024, 15 (1), 6764.). Estimated total BC emissions are 205 (+55.0, −127) Gg and 247 (+50.0, −154) Gg for the mass- and number-conserved methods, respectively, exceeding FINN and EDGAR-HTAP inventory values by factors of 15.0 and 18.2, but of similar magnitude to regional average top-down studies (Cohen, J. B.; Wang, C. Estimating global black carbon emissions using a top-down Kalman Filter approach. J. Geophys. Res.: Atmos. 2014, 119 (1), 307−323. Chen, C., Multi-angular polarimetric remote sensing to pinpoint global aerosol absorption and direct radiative forcing. Nat. Commun. 2022, 13 (1), 7459.). These higher estimates stem from improved identification of spatially and temporally missing sources and correction of underestimated emissions. The number-conservative method yields 16.5% and 30.3% more emissions than the mass-based approach in BB and urban areas, underscoring the importance of particle number in characterizing BC. Daily uncertainty ranges of 22.7–64.2% and 23.3–62.3% indicate that better constraints on BC size distribution are critical for improving top-down emission estimates.