1. Atmospheric Aerosol Research Department, Institute for Meteorology and Climate Research (IMK-AAF), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
2. Laboratory for Electron Microscopy (LEM), KIT, Engesserstrasse 7, 76131 Karlsruhe, Germany.
3. London Centre for Nanotechnology, Thomas Young Centre, and Department of Chemistry, University College London (UCL), 17-19 Gordon Street, London WC1H 0AH, UK.
4. London Centre for Nanotechnology, Thomas Young Centre, and Department of Physics and Astronomy, UCL, 17-19 Gordon Street, London WC1H 0AH, UK.
5. Institut für Umweltphysik, Universität Heidelberg, Im Neuenheimer Feld 229, Heidelberg, Germany.