Aerosol-Cloud Interaction Studies Conducted during the DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) Field Campaign

The EU-funded project DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) is investigating the relationship between weather, climate, and air pollution in southern West Africa. The air over the coastal region of West Africa is a unique mixture of natural and anthropogenic gases, liquids, and particles, emitted in an environment, in which multi-layer cloud decks frequently form. These exert a large influence on the local weather and climate, mainly due to their impact on radiation, the surface energy balance, and thus the diurnal cycle of the atmospheric boundary layer. The composition of the particles in the air – and their impact on the formation and breakup of clouds – has never been studied in detail over West Africa and this information is currently not included in the majority of weather and climate models in such a complex chemical environment.

For the first time, the entire chain of impacts of natural and manmade emissions on the West African atmosphere was investigated in a coordinated field campaign. As part of this campaign, three research aircraft based in Lomé (Togo) flew targeted missions over West Africa from 27 June to 16 July 2016. The three research aircraft involved are the Falcon 20 of the Deutsches Zentrum für Luft- und Raumfahrt (German Aerospace Center), the Twin Otter of the British Antarctic Survey, and the French ATR operated by the Service des Avions Français Instrumentés pour la Recherche en Environnement. In addition, DACCIWA scientists set up three highly instrumented supersites inland, launched weather balloons several times a day across the region, measured urban emissions, and evaluated health data.

As part of the DACCIWA field campaign, the three aircraft conducted a total of 50 research flights across Ivory Coast, Ghana, Togo, and Benin, 23 of which dedicated to aerosol-cloud interactions. The main objective was to build robust statistics of cloud properties in southern West Africa in different chemical landscapes: from the background state over the Gulf of Guinea (marine aerosols or mix between marine aerosols and biomass burning aerosols) to ship/flaring emissions to the coastal strip of polluted megacities to the agricultural areas and forest areas further north, and eventually dust from the Sahel/Sahara. Concomitantly, the three supersites in Ghana, Benin, and Nigeria conducted 15 Intensive Observation Periods (over two months) to investigate the processes involved in the life cycle of low-level clouds.

First highlights from the airborne and surface-based observations, together with accompanying modelling work, will be presented.