now at: Institute of Agricultural Sciences, ETH-Zürich, Switzerland

Invited contribution by L. Hörtnagl, recipient of the EGU Outstanding Student Poster (OSP) Award 2011.

Institute of Ecology, University of Innsbruck, Austria

now at: Institute of Agricultural Sciences, ETH-Zürich, Switzerland

Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria

now at: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA

now at: Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USA

Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria

currently at: Division of Atmospheric Sciences, University of Helsinki, Finland

Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria

Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria

now at: Engineering Exhaust Gas Sensors, Robert Bosch GmbH, Stuttgart, Germany

Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria

Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria

Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria

Institute of Ecology, University of Innsbruck, Austria