Impact of biomass burning on pollutants surface concentrations in megacities of the Gulf of Guinea

Abstract : In the framework of the "Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa" (DACCIWA) project, the tropospheric chemical composition in the megacities along the Guinean Gulf is studied using the Weather and Research Forecast and CHIMERE regional models. Simulations are performed for the May–July 2014 period, without and with biomass burning emissions. Model results are compared to satellite data and surface measurements. Using numerical tracer release experiments, it is shown that the fire emissions in Central Africa are impacting the surface aerosol and gaseous species concentrations in the Guinean Gulf cities, such as Lagos (Nigeria) and Abidjan (Ivory Coast). Depending on the altitude of injection of these emissions, the pollutants follow different pathways: directly along the coast or over land towards the Sahel before to be vertically mixed in the convective boundary layer and transported to the south-west and over the cities. In July 2014, the maximum increase in surface concentrations is ~ 150 μg m⁻³ for CO, ~ 10 to 20 μg m⁻³ for O₃ and ~ 5 μg m⁻³ for PM₁₀. The analysis of the PM₁₀ chemical composition shows that this increase is mainly related to an increase of Particulate Primary Matter and Particulate Organic Matter.