Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 6 2005 10.5194/acpd-5-11277-2005 http://www.atmos-chem-phys-discuss.net/5/11277/2005/ http://www.atmos-chem-phys-discuss.net/5/11277/2005/acpd-5-11277-2005.html http://www.atmos-chem-phys-discuss.net/5/11277/2005/acpd-5-11277-2005.pdf 11277 11293 2005-11-08 Why formation rate of 3 nm particles depends linearly on sulphuric acid concentration? M. Kulmala markku.kulmala@helsinki.fi K. E. J. Lehtinen A. Laaksonen University of Helsinki, Department of Physical Sciences, P.O. Box 64, FIN-00014 Helsinki, Finland Finnish Meteorological Institute and University of Kuopio, Department of Applied Physics, P.O. Box 1627, FIN-70211 Kuopio, Finland University of Kuopio, Department of Applied Physics, P.O. Box 1627, FIN-70211 Kuopio, Finland According to atmospheric observations new particle formation seems to be a function of sulphuric acid concentration to the power from one to two. The nucleation theorem then predicts that the critical cluster contains one to two sulphuric acid molecules. However, existing nucleation theories predicts that the power is more (or equal) than 2. Here we present an activation theory, which can explain the observed slope. In cluster activation the clusters containing one sulphuric acid molecule will activate for further growth due to heterogeneous nucleation, heterogeneous chemical reactions including polymerization or activation of soluble clusters. In the activation process organic vapours are typically needed as condensing agents.