Influence of biogenic NO emissions from soil on Atmospheric chemistry over Africa: a regional modelling study

Abstract. In the context of climate change and increasing anthropogenic pressures in Africa, understanding the interactions between atmospheric chemistry, regional climate, and biogeochemical cycles is critical. This study investigates the potential role of biogenic nitric oxide emissions from African soils (BioNO), particularly in arid and semi-arid ecosystems, as significant contributors to atmospheric NO₂ emissions and regional atmospheric chemistry. To this end, we rely on a modelling approach based on the RegCM5 regional climate model, including an updated atmospheric chemistry module and, amongst other, a specific parametrization for BioNO emissions. Throughout the paper, the model performances are evaluated against various datasets including in-situ observations from the INDAAF network and chemical reanalyses. Sensitivity studies demonstrate that integrating BioNO emissions into the model enhances the accuracy of simulated NO₂, HNO₃, and O₃ seasonal cycles and surface concentration magnitudes, while reducing simulated biases against ground based observations. Large differences are however still present regarding notably the simulated surface ozone concentration magnitude vs in situ measurements, while these biases are also observed for chemical reanalyses, and a state of the art chemistry transport model used for comparison. Beside outlining the impact and added value of BioNO flux representation for regional atmospheric chemistry, our findings also outline the suitability of RegCM5 coupled system for the study of regional climate, chemistry and nitrogen cycle interactions over Africa.