ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-11-15875-2011 Measurements of aerosol charging states in Helsinki, Finland Gagné S. 1 Leppä J. 2 Petäjä T. 1 McGrath M. J. 1 Vana M. 1 3 Kerminen V.-M. 2 Laakso L. 1 2 4 Kulmala M. 1 Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland Finnish Meteorological Institute, Climate Change, P.O. Box 503, 00101 Helsinki, Finland Institute of Physics, University of Tartu, Ülikooli 18, 50090 Tartu, Estonia School of Physical and Chemical Sciences, North-West University, Private Bag x6001, Potchefstroom 2520, South Africa 26 05 2011 11 5 15875 15920 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-discuss.net/11/15875/2011/acpd-11-15875-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/11/15875/2011/acpd-11-15875-2011.pdf

The charging state of aerosol populations was measured with an Ion-DMPS in Helsinki, Finland between December 2008 and February 2010. Based on the charging states, we calculated the ion-induced nucleation fraction to be around 0.8 % ± 0.9 %. We review the role of ion-induced nucleation and propose different explanations for a low ion-induced nucleation participation in urban areas. We present a new method to retrieve the average charging state for an event, and a given size. We also use a new theoretical framework that allows for different concentrations of small cluster ions for different polarities (polarity asymmetry). We extrapolate the ion-induced fraction using polarity symmetry and asymmetry. Finally, a method to calculate the growth rates from the variation of the charging state as a function of the particle diameter using polarity symmetry and asymmetry is presented and used on a selection of new particle formation events.

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