"Massive economic and population growth and urbanisation are expected to lead to a tripling of anthropogenic emissions in southern West Africa (SWA) between 2000 and 2030, the impacts of which on human health, ecosystems, food security and the regional climate are largely unknown. An assessment of these impacts is complicated by (a) a superposition with effects of global climate change, (b) the strong dependence of SWA on the sensitive West African monsoon, (c) incomplete scientific understanding of interactions between emissions, clouds, radiation, precipitation and regional circulations and (d) by a lack of observations to advance our understanding and improve predictions. The DACCIWA project will conduct extensive fieldwork in SWA to collect high-quality observations, spanning the entire process chain from surface-based natural and anthropogenic emissions to impacts on health, ecosystems and climate. Combining the resulting benchmark dataset with a wide range of modelling activities will allow (a) to assess all relevant physical and chemical processes, (b) to improve the monitoring of climate and compositional parameters from space and (c) to develop the next generation of weather and climate models capable of representing coupled cloud-aerosol interactions, which will ultimately lead to reduced uncertainties in climate predictions. SWA with its rich mix of emissions and diverse clouds is ideal for such a study and many findings and technical developments will be applicable to other monsoon regions. Using a targeted dissemination strategy, DACCIWA will deliver a comprehensive scientific assessment and actively guide sustainable future planning and policy-making for West Africa and beyond. The interdisciplinary and experienced DACCIWA team will build on the scientific and logistical foundations established by AMMA (EU FP6) and collaborate closely with operational centres, international programs (e.g. WCRP, IGBP), policy-makers and users to maximise impact."