Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 4 2006 10.5194/acpd-6-6401-2006 http://www.atmos-chem-phys-discuss.net/6/6401/2006/ http://www.atmos-chem-phys-discuss.net/6/6401/2006/acpd-6-6401-2006.html http://www.atmos-chem-phys-discuss.net/6/6401/2006/acpd-6-6401-2006.pdf 6401 6429 2006-07-13 Detecting charging state of ultra-fine particles: instrumental development and ambient measurements L. Laakso S. Gagné T. Petäjä A. Hirsikko P. P. Aalto M. Kulmala V.-M. Kerminen Department of Physical Sciences, P.O. Box 64, 00014, University of Helsinki, Finland Finnish Meteorological Institute, Air Quality Research, P.O. BOX 503, 00101 Helsinki, Finland The importance of ion-induced nucleation in the lower atmosphere has been discussed for a long time. In this article we describe a new instrumental setup – Ion-DMPS – which can be used to detect contribution of ion-induced nucleation on atmospheric new particle formation events. We performed several laboratory tests to test the operation of the device and then we measured atmospheric new particle formation events with the instrument in a boreal forest. We found that some of the events were clearly dominated by neutral nucleation but in some cases also ion-induced nucleation contributed to the new particle formation. We also found that negative and positive ions behaved in a different manner, days with negative overcharging were more frequent than days with positive overcharging. A simple order of magnitude estimate gave the contribution of ion-induced nucleation on total nucleation approximately 10%. During the neutral-dominated nucleation days ion contribution was close to zero.