1. Laboratory of Atmospheric Chemistry; Paul Scherrer Institute (PSI); Villigen CH-5232 Switzerland
2. Swiss Federal Institute for Forest, Snow and Landscape Research WSL; Birmensdorf CH-8903 Switzerland
3. Institute of Agricultural Sciences; ETH Zurich; Zurich CH-8092 Switzerland
4. Department of Environmental Sciences - Botany; University of Basel; Basel CH-4056 Switzerland