Max Planck Institute for Chemistry, Department of Biogeochemistry, P.O. Box 3060, 55020 Mainz, Germany

now at: GSF-Research Center for Environment and Health, Institute for Inhalation Biology, P.O. Box 1129, 85758 Neuherberg/Munich, Germany

University of São Paulo, Institute of Physics, São Paulo, Brazil

Desert Research Institute, Division of Atmospheric Science, Reno, NV, USA

Max Planck Institute for Chemistry, Department of Biogeochemistry, P.O. Box 3060, 55020 Mainz, Germany

Institute of Nuclear Energy Research, Atmospheric Chemistry Laboratory, São Paulo, SP, Brazil

Max Planck Institute for Chemistry, Department of Biogeochemistry, P.O. Box 3060, 55020 Mainz, Germany

Max Planck Institute for Chemistry, Department of Biogeochemistry, P.O. Box 3060, 55020 Mainz, Germany

Research Center Karlsruhe, Institute of Meteorology and Climate Research, P.O.~Box 3640, 76021 Karlsruhe, Germany

Max Planck Institute for Chemistry, Department of Biogeochemistry, P.O. Box 3060, 55020 Mainz, Germany