1Finnish Meteorological Institute, Air Quality Research, Sahaajankatu 20E, FIN-00880 Helsinki, Finland
2University of Helsinki, Department of Physical Sciences, P.O. Box 64, FIN-00014 University of Helsinki, Helsinki, Finland
3University of Kuopio, Department of Applied Physics, P.O. Box 1627, FIN-70211, Kuopio, Finland
4Department of Experimental Physics, National University of Ireland, Galway, University Road, Galway, Ireland
Abstract. Particle formation resulting from activation of inorganic stable clusters by a supersaturated organic vapour was investigated using a numerical model. The applied aerosol dynamic model included a detailed description of the activation process along with a treatment of the appropriate aerosol and gas-phase processes. The obtained results suggest that both gaseous sulphuric acid and organic vapours contribute to organic particle formation in continental background areas. The initial growth of freshly-nucleated clusters is driven mainly by condensation of gaseous sulphuric acid and by a lesser extent self-coagulation. After the clusters have reached sizes of around 2 nm in diameter, low-volatile organic vapours start to condense spontaneously into the clusters, thereby accelerating their growth to detectable sizes. A shortage of gaseous sulphuric acid or organic vapours limit, or suppress altogether, the particle formation, since freshly-nucleated clusters are rapidly coagulated away by pre-existing particles. The obtained modelling results were applied to explaining the observed seasonal cycle in the number of aerosol formation events in a continental forest site.