ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-1071-2004 Modelling the formation of organic particles in the atmosphere Anttila T. 1 2 Kerminen V.-M. 1 Kulmala M. 2 Laaksonen A. 3 O'Dowd C. D. 4 Finnish Meteorological Institute, Air Quality Research, Sahaajankatu 20E, FIN-00880 Helsinki, Finland University of Helsinki, Department of Physical Sciences, P.O. Box 64, FIN-00014 University of Helsinki, Helsinki, Finland University of Kuopio, Department of Applied Physics, P.O. Box 1627, FIN-70211, Kuopio, Finland Department of Experimental Physics, National University of Ireland, Galway, University Road, Galway, Ireland 06 07 2004 4 4 1071 1083 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/4/1071/2004/acp-4-1071-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/1071/2004/acp-4-1071-2004.pdf

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.