Abstract
Abstract. The aerosol direct and indirect effects are studied over west Africa in the summer of 2016 using the coupled WRF-CHIMERE regional model including aerosol–cloud interaction parameterization. First, a reference simulation is performed and compared with observations acquired during the Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) field campaign which took place in June and July 2016. Sensitivity experiments are also designed to gain insights into the impact of the aerosols dominating the atmospheric composition in southern west Africa (one simulation with halved anthropogenic emissions and one with halved mineral dust emissions). The most important effect of aerosol–cloud interactions is found for the mineral dust scenario, and it is shown that halving the emissions of mineral dust decreases the 2 m temperature by 0.5 K and the boundary layer height by 25 m on a monthly average (July 2016) and over the Saharan region. The presence of dust aerosols also increases (decreases) the shortwave (longwave) radiation at the surface by 25 W m−2. It is also shown that the decrease of anthropogenic emissions along the coast has an impact on the mineral dust load over west Africa by increasing their emissions in the Saharan region. It is due to a mechanism where particulate matter concentrations are decreased along the coast, imposing a latitudinal shift of the monsoonal precipitation and, in turn, an increase of the surface wind speed over arid areas, inducing more mineral dust emissions.
Highlights
Megacities in the Gulf of Guinea are under frequent and intense air pollution episodes, with pollutants mostly originating from local anthropogenic emissions as well as form a variety of remote sources such as the Sahara and the Sahel, and central Africa
The months of June–July 2016 were modelled using the Weather and Research Forecasting (WRF)-CHIMERE regional models over a large domain centred on the Gulf of Guinea
The modelled period corresponds to the Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) intensive observation periods
Summary
Megacities in the Gulf of Guinea are under frequent and intense air pollution episodes, with pollutants mostly originating from local anthropogenic emissions as well as form a variety of remote sources such as the Sahara and the Sahel (mineral dust), and central Africa (biomass burning products) This atmospheric pollution has an impact on human health (Bauer et al, 2019) and climate and, in the short term, on meteorology and radiation through the direct and indirect effects of aerosols (Haywood and Boucher, 2000; Andreae and Rosenfeld, 2008). In the framework of the DACCIWA project, the impact of long-range transport of dust and biomass burning on surface pollution (gas and aerosols) was quantified using measurements and the WRF-CHIMERE model in Menut et al (2018) This was done without taking into account the interactions between aerosols and clouds, and for the summer of 2014, so a comparison with extensive measurements was not possible.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
