ILAQH, Queensland University of Technology, P.O. Box 4233, Brisbane QLD, 4001, Australia

Div. of Atmospheric Sciences and Geophysics, Department of Physics, University of Helsinki, P.O. Box 64, 00014, Finland

Div. of Atmospheric Sciences and Geophysics, Department of Physics, University of Helsinki, P.O. Box 64, 00014, Finland

Div. of Atmospheric Sciences and Geophysics, Department of Physics, University of Helsinki, P.O. Box 64, 00014, Finland

ILAQH, Queensland University of Technology, P.O. Box 4233, Brisbane QLD, 4001, Australia

now at: Laboratory for Energy Systems Analysis, Paul Scherrer Institut, 5232 Villigen, Switzerland

Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen, Switzerland

now at: Physic Department, CERN, 1211, Switzerland

ANCAR/ACD, BAI Group, 3450 Mitchell Lane, Boulder, CO 80301, USA

ILAQH, Queensland University of Technology, P.O. Box 4233, Brisbane QLD, 4001, Australia

Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen, Switzerland