BACCHUS (http://www.bacchus-env.eu/) is a European FP7 Collaborative Project aiming at quantifying key processes and feedbacks that control aerosol–cloud interactions by combining advanced measurement techniques of cloud and aerosol properties with emphasis on ice nucleating particles and the ice phase in clouds with state-of-the-art numerical modelling. It investigates the importance of biogenic versus anthropogenic emissions for aerosol–cloud interactions in regions that are key regulators of Earth's climate (Amazonian rainforest) or are regarded as tipping elements in the climate system (Arctic). BACCHUS advances the understanding of biosphere aerosol–cloud–climate feedbacks that occur via emission and transformation of biogenic volatile organic compounds, primary biological aerosols, secondary organic aerosols, and dust. New fundamental understanding gained during BACCHUS will be incorporated into Earth system models through new or improved parameterizations of emissions, aerosol and cloud processes, and properties, which will lead to a reduction in the uncertainty of future climate projections. A unique database linking long-term observations and field campaign data of ice nucleating particles and observed cloud microphysical properties has been generated.

The BACCHUS special issue will be simultaneously presented in the ACP, AMT, and GMD journals and is open for all submissions acknowledging the BACCHUS project. BACCHUS is a collaborative project of 21 partner institutions: ETH Zurich, University of Helsinki, Paul Scherrer Institute, Max Planck Society (MPI-M, MPI-C), University of Oxford, University of Oslo, Finnish Meteorological Institute, University of Leeds, University of Manchester, Leibniz Institute for Tropospheric Research, Goethe University Frankfurt, the University of Crete, National Research Council of Italy – Institute of Atmospheric Sciences and Climate, National University of Ireland Galway, Institute for Nuclear Research and Nuclear Energy, Hebrew University of Jerusalem, National Center for Scientific Research (France), Karlsruhe Institute of Technology, Cyprus Institute, Cyprus University of Technology, and University of Gothenburg. The project is funded by the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 603445.