Kinetic nucleation and ions in boreal forest particle formation events L. Laakso1, T. Anttila1,3, K. E. J. Lehtinen1, P. P. Aalto1, M. Kulmala1, U. Hõrrak2, J. Paatero3, M. Hanke4, and F. Arnold4 1Department of Physical Sciences, P.O. Box 64, FIN-00014 University of Helsinki, Finland 2Institute of Environmental Physics, University of Tartu, 18 Ülikooli Street, Tartu, 50090, Estonia 3Finnish Meteorological Institute, Air Quality Research, Sahaajankatu 20E, FIN-00880 Helsinki, Finland 4Max-Planck-Institute für Kernphysik (MPI-K), D-6900 Heidelberg, P.O. Box 103980, Germany
Abstract. In order to gain a more comprehensive picture on different mechanisms behind
atmospheric particle formation, measurement results from QUEST 2-campaign
are analyzed with an aid of an aerosol dynamic model. A special emphasis
is laid on air ion and charged aerosol dynamics. Model simulations indicate
that kinetic nucleation of ammonia and sulphuric acid together with
condensation of sulphuric acid and low-volatile organic vapours onto
clusters and particles explain basic features of particle
formation events as well as ion characteristics. However,
an observed excess of negative ions in the diameter range 1.5-3nm
and overcharge of 3-5nm particles demonstrate that ions are also involved
in particle formation. These observations can be explained by
preferential condensation of sulphuric acid
onto negatively charged clusters and particles
and/or contribution of ion-induced nucleation on particle formation.
According to model simulations, which assume that the nucleation
rate is equal to the sulfuric acid collision rate, the relative contribution of ion-based
particle formation seems to be smaller than kinetic nucleation of neutral clusters.
Conducted model simulations also corroborate the recently-presented hypothesis according
to which a large number of so-called
thermodynamically stable clusters (TSCs) having a diameter between 1-3nm
exist in the atmosphere. TSCs were found to grow to observable sizes
only under favorable conditions, e.g. when the pre-existing particle
concentration was low.
Citation: Laakso, L., Anttila, T., Lehtinen, K. E. J., Aalto, P. P., Kulmala, M., Hõrrak, U., Paatero, J., Hanke, M., and Arnold, F.: Kinetic nucleation and ions in boreal forest particle formation events, Atmos. Chem. Phys., 4, 2353-2366, doi:10.5194/acp-4-2353-2004, 2004.