ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-1933-2004 Ion production rate in a boreal forest based on ion, particle and radiation measurements Laakso L. 1 Petäjä T. 1 Lehtinen K. E. J. 1 Kulmala M. 1 Paatero J. 2 Hõrrak U. 3 Tammet H. 3 Joutsensaari J. 4 Department of Physical Sciences, P.O. Box 64, FI-00014 University of Helsinki, Finland Finnish Meteorological Institute, Air Quality Research, Sahaajankatu 20E, FIN-00880 Helsinki, Finland Institute of Environmental Physics, University of Tartu, 18 Ülikooli Street, Tartu, 50090, Estonia Department of Applied Physics, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland 29 09 2004 4 7 1933 1943 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/4/1933/2004/acp-4-1933-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/1933/2004/acp-4-1933-2004.pdf

In this study the ion production rates in a boreal forest were studied based on two different methods: 1) cluster ion and particle concentration measurements, 2) external radiation and radon concentration measurements. Both methods produced reasonable estimates for ion production rates. The average ion production rate calculated from aerosol particle size distribution and air ion mobility distribution measurements was 2.6 ion pairs cm<sup>-3</sup>s<sup>-1</sup>, and based on external radiation and radon measurements, 4.5 ion pairs cm<sup>-3</sup>s<sup>-1</sup>. The first method based on ion and particle measurements gave lower values for the ion production rates especially during the day. A possible reason for this is that particle measurements started only from 3nm, so the sink of small ions during the nucleation events was underestimated. It may also be possible that the hygroscopic growth factors of aerosol particles were underestimated. Another reason for the discrepancy is the nucleation mechanism itself. If the ions are somehow present in the nucleation process, there could have been an additional ion sink during the nucleation days.