Seaports in Africa are expanding rapidly to meet an increasing demand for imported goods in Africa and for natural resources and manufactured goods from the continent. Emissions from shipping and anthropogenic activities at seaports, in particular nitrogen oxides (NO_x), are challenging to estimate. This impacts our ability to determine the impacts of shipping activities on ozone air pollution for a continent that is NO_x limited. Here we develop an approach to oversample tropospheric column observations of nitrogen dioxide (NO₂) from the recently launched high spatial resolution TROPOMI instrument to determine NO_x emissions from shipping activities at major seaports along the African coastline from August 2019 to July 2020. We use these to evaluate state-of-science emission inventories and determine temporal variability in these emissions for improved implementation in global and regional models.