MAX-DOAS measurements of AOT, NO2 and HCHO in Kinshasa (DR Congo): comparisons with TROPOMI and GEOS-CHEM

African megacities suffer from air pollution and the problem is expected to worsen in the near-future, with the ongoing explosive demographic growth in these areas. The sources of pollutants in Africa are different from those found in Europe. Agricultural burnings and charcoal-based cooking largely contribute to the NO2 and HCHO burdens. However, many large African cities, such as the City of Kinshasa, capital of the Democratic Republic of Congo, do not have local pollution monitoring capabilities. In these polluted places, space-based measurements are often the only source of data available regarding air quality. Together with the validation of TROPOMI in a poorly sampled area, this context motivated ground-based DOAS observations in Kinshasa since 2017. We first operated a single-axis instrument, which we upgraded as a MAX-DOAS instrument in December 2019.  

We describe the observation site in Kinshasa, the MAX-DOAS instrument, and the retrievals which use the algorithmic tools developed within the FRM4DOAS project. We compare the MAX-DOAS database (2019-2023) of ground-based observations of aerosol optical thickness (AOT), NO2 and HCHO with MODIS and TROPOMI, and with simulations using the GEOS-CHEM Chemistry and Transport Model. Such comparisons enable to assess the quality of the satellite products and model performances around Kinshasa. The ground and satellite-based observations have different sensitivities to the trace gas profiles. Combining the observations and model datasets sheds light on the true atmospheric state above Kinshasa. Another objective of this work is to constrain emission inventories in central Africa.