Initial steps of aerosol growth M. Kulmala1, L. Laakso1, K. E. J. Lehtinen1, I. Riipinen1, M. Dal Maso1, T. Anttila1,2, V.-M. Kerminen2, U. Hõrrak1,3, M. Vana1,3, and H. Tammet3 1Department of Physical Sciences, Division of Atmospheric Sciences P.O. Box 64, FIN-00014 University of Helsinki, Finland 2Finnish Meteorological Institute, Air Quality Research Sahaajankatu 22E, FIN-00880 Helsinki, Finland 3Institute of Environmental Physics, University of Tartu, Ülikooli 18, 50090 Tartu, Estonia
Abstract. The formation and growth of atmospheric aerosols depend on several steps,
namely nucleation, initial steps of growth and subsequent – mainly
condensational – growth. This work focuses on the initial steps of growth,
meaning the growth right after nucleation, where the interplay of curvature
effects and thermodynamics has a significant role on the growth kinetics.
More specifically, we investigate how ion clusters and aerosol particles
grow from 1.5 nm to 20 nm (diameter) in atmospheric conditions using
experimental data obtained by air ion and aerosol spectrometers. The
measurements have been performed at a boreal forest site in Finland. The
observed trend that the growth rate seems to increase as a function of size
can be used to investigate possible growth mechanisms. Such a growth rate is
consistent with a recently suggested nano-Köhler mechanism, in which growth
is activated at a certain size with respect to condensation of organic
vapors. The results also imply that charge-enhanced growth associated with
ion-mediated nucleation plays only a minor role in the initial steps of
growth, since it would imply a clear decrease of the growth rate with size.
Finally, further evidence was obtained on the earlier suggestion that
atmospheric nucleation and the subsequent growth of fresh nuclei are likely
to be uncoupled phenomena via different participating vapors.
Citation: Kulmala, M., Laakso, L., Lehtinen, K. E. J., Riipinen, I., Dal Maso, M., Anttila, T., Kerminen, V.-M., Hõrrak, U., Vana, M., and Tammet, H.: Initial steps of aerosol growth, Atmos. Chem. Phys., 4, 2553-2560, doi:10.5194/acp-4-2553-2004, 2004.