Open Access

Mikko Sipilä, Katrianne Lehtipalo, Markku Kulmala, Tuukka Petäjä, Heikki Junninen, Pasi Aalto, Hanna Elina Manninen, E. Vartianinen, Ilona Riipinen, Ella-Maria Kyrö, Joachim Curtius, Christoph Andreas Kürten, Stephan Borrmann, Colin D. O'Dowd

• The ambient and laboratory molecular and ion clusters were investigated. Here we present data on the ambient concentrations of both charged and uncharged molecular clusters as well as the performance of a pulse height condensation particle counter (PH-CPC) and an expansion condensation particle counter (E-CPC). The ambient molecular cluster concentrations were measured using both instruments, and they were deployed in conjunction with ion spectrometers and other aerosol instruments in Hyytiälä, Finland at the SMEAR II station during 1 March to 30 June 2007. The observed cluster concentrations varied and were from ca. 1000 to 100 000 cm−3. Both instruments showed similar concentrations. The average size of detected clusters was approximately 1.8 nm. As the atmospheric measurements at sub 2-nm particles and molecular clusters are a challenging task, and we were most likely unable to detect the smallest clusters, the reported concentrations are our best estimates for minimum cluster concentrations in boreal forest environment.