Urban and Power Plant NO _<i>x</i> Emissions in Sub‐Saharan Africa Inferred From TROPOMI

Abstract Nitrogen oxides (NO x ) emissions are increasing rapidly in Sub‐Saharan Africa, affecting local air quality. Outside South Africa, most hotspots are relatively small, posing a challenge for traditional top‐down inversions. We tailor an existing top‐down wind rotation and Gaussian plume fit inversion to suit the relatively small NO x hotspots for most of Sub‐Saharan Africa. We apply the customized inversion to 3 years (July 2018–December 2019 and January 2021–June 2022) of nitrogen dioxide (NO 2 ) observations from the Tropospheric Monitoring Instrument (TROPOMI) to derive annual NO x emissions for 24 isolated hotspots (21 urban, three power plants) compared to at most 5 for Sub‐Saharan Africa in past global studies. Annual hotspot emissions total 311.5 kt NO. Urban hotspot emissions range from &lt;2 mol s −1 for Antananarivo, Madagascar, to 27.7 ± 12.6 mol s −1 for the megacity Lagos in Nigeria. Coal‐fired power plant emissions are 2.7 ± 1.0 mol s −1 for Hwange, Zimbabwe, and similar (∼70 mol s −1 ) for Lethabo and combined Matimba and Medupi plumes in South Africa. Top‐down estimates are 8%–20% less than Continuous Emissions Monitoring Systems emissions. We conduct a quasi‐independent evaluation of urban top‐down emissions by assessing improved agreement between the GEOS‐Chem model and TROPOMI NO 2 after updating modeled emissions to match the top‐down estimates. Annual urban inventory hotspot emissions decline by 43 kt NO and the model root mean squared error is more than halves from 1.2 × 10 15 molecules cm −2 to 0.48 × 10 15 molecules cm −2 . Our top‐down emissions exhibit large, up to six‐fold, systematic differences with contemporary global and regional inventories.