1. Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
2. Oeschger Centre for Climate Change Research, University of Bern, CH-3012 Bern, Switzerland.
3. Department for Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland.
4. Climate and Environmental Physics, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland.