HALO-(AC)³ is a research campaign jointly performed by the University Leipzig, the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, the German Aerospace Center, the Laboratoire de Météorologie Physique France, the Leibniz Institute for Tropospheric Research, the Max Planck Institutes for Meteorology in Hamburg and for Chemistry in Mainz as well as the Universities of Bremen, Hamburg and Cologne, and the Ludwig Maximilian University of Munich. The German Research Foundation supports this campaign via the Transregional Collaborative Research Center (AC)³ and the Priority Program HALO.