1Air Chemistry Department, Max-Planck Institute of Chemistry, Mainz, Germany
2Plant and Vegetation Ecology, University of Antwerp, Wilrijk, Belgium
3Faculty of Chemistry, University of Sciences and Technology Houari Boumediene, Algiers, Algeria
4Department of Physics, University of Helsinki, Helsinki, Finland
5Atmospheric trace gases, Institute of Atmospheric Physics, DLR, Oberpfaffenhofen-Wessling, Germany
6Atmospheric Trace Gases and Ions, Max-Planck-Institute for Nuclear Physics, Heidelberg, Germany
Abstract. In this study we present measurements of selected trace gases and aerosol made in a boreal forest during the BACCI-QUEST IV intensive field campaign in Hyytiälä, Finland in April 2005. Several clear aerosol "nucleation events" were observed and characterized. One type of "event" occurred synchronously with huge increases in monoterpenes, while a second event type correlated instead with sulphuric acid. Here we elucidate the origin of these two distinct forms of aerosol production at the Hyytiälä site using the measurement data, airmass back trajectories and the optical stereoisomery of monoterpenes.