Abstract
Abstract. In the framework of the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) project, the tropospheric chemical composition in large cities along the Gulf of Guinea 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 biomass burning emissions in Central Africa are impacting the surface aerosol and gaseous species concentrations in Gulf of Guinea cities such as Lagos (Nigeria) and Abidjan (Ivory Coast). Depending on the altitude of the injection of these emissions, the pollutants follow different pathways: directly along the coast or over land towards the Sahel before being 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 due to fires in Central Africa 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 in particulate primary and organic matter.
Highlights
The concentrations of gases and particles are rapidly growing in southern West Africa (SWA) and driven by the constant increase in anthropogenic atmospheric emissions
The goal of this study is to quantify the relative contribution of the pollutants associated with biomass burning from Central Africa on the surface concentrations of aerosols, carbon monoxide (CO), and ozone (O3) in urbanized areas pertaining to the Dynamics–Aerosol– Chemistry–Cloud Interactions in West Africa (DACCIWA) project
The four emitted tracers provide non-zero surface concentrations on the three sites. This means that the meteorological conditions are favourable to the transport of biomass burning from Central Africa to the Gulf of Guinea
Summary
The concentrations of gases and particles are rapidly growing in southern West Africa (SWA) and driven by the constant increase in anthropogenic atmospheric emissions These emissions are linked with car traffic, industries, and related gas and oil extraction activities, domestic fires, and waste burning (Marais and Wiedinmyer, 2016). The atmospheric pollution problems are mainly present along the coast of the Gulf of Guinea spanning from Abidjan (Ivory Coast) to Port Harcourt (Nigeria) and occur in the lower few hundred metres above the surface in the atmospheric boundary layer (ABL) In addition to this anthropogenic regional pollution, the region is impacted by other important sources, especially in the summer, with large emissions of mineral dust from the Sahara and the Sahel to the north and vegetation fires from Central and southern Africa (Real et al, 2010). Using a Lagrangian model, Mari et al (2008) show that the intrusion of Southern Hemispheric biomass burning aerosol plumes occurred in the mid-troposphere over the Gulf of Guinea, but did not investigate whether these plumes could impact air quality over urbanized areas of SWA
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