1. Institut für Umweltphysik, University of Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany
2. Alfred Wegener Institute for Polar and Marine Research, D-27570 Bremerhaven, Germany
3. Vienna Environmental Research Accelerator, University of Vienna, A-1090 Vienna, Austria
4. Laboratory for Ion Beam Physics, ETH-Zurich, CH-8093 Zurich, Switzerland