Analysis of atmospheric neutral and charged molecular clusters in boreal forest using pulse-height CPC
- 1Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland
- 2Helsinki Institute of Physics, P.O. Box 64, 00014 University of Helsinki, Finland
Abstract. We measured the size distribution of atmospheric neutral and charged clusters and particles down to mobility diameter around 1.5 nm by applying pulse-height CPC technique at SMEAR II station in Hyytiälä, southern Finland during spring 2007 and May 2008. The concentration of molecular clusters smaller than 3 nm seems to be highly variable in boreal forest environment, the concentration varied typically between 500–50 000 cm−3. By comparing to concentrations measured with ion spectrometers, we conclude that ion clusters and neutral clusters produced by ion-ion recombination are usually not sufficient to explain all of the observed clusters; the median fraction of recombination products from all neutral clusters was 4.9%. Before and during most new particle formation events the cluster formation rate rose only slightly, or remained close to stable. Nocturnal formation of clusters was also frequently observed.