1Tampere University of Technology, Department of Physics, P.O. Box 692, 33101 Tampere, Finland
2University of Eastern Finland, Department of Applied Physics, P.O. Box 1627, 70211 Kuopio, Finland
3University of Eastern Finland, Department of Environmental Science, P.O. Box 1627, 70211 Kuopio, Finland
4Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
5Aerodyne Research, Billerica, MA 08121-3976, USA
6Finnish Meteorological Institute, P.O. Box 1627, Kuopio, Finland
7National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307, USA
Abstract. The assessment of the climatic impacts and adverse health effects of atmospheric aerosol particles requires detailed information on particle properties. However, very limited information is available on the morphology and phase state of secondary organic aerosol (SOA) particles. The physical state of particles greatly affects particulate-phase chemical reactions, and thus the growth rates of newly formed atmospheric aerosol. Thus verifying the physical phase state of SOA particles gives new and important insight into their formation, subsequent growth, and consequently potential atmospheric impacts. According to our recent study, biogenic SOA particles produced in laboratory chambers from the oxidation of real plant emissions as well as in ambient boreal forest atmospheres can exist in a solid phase in size range >30 nm. In this paper, we extend previously published results to diameters in the range of 17–30 nm. The physical phase of the particles is studied by investigating particle bounce properties utilizing electrical low pressure impactor (ELPI). We also investigate the effect of estimates of particle density on the interpretation of our bounce observations. According to the results presented in this paper, particle bounce clearly decreases with decreasing particle size in sub 30 nm size range. The comparison measurements by ammonium sulphate and investigation of the particle impaction velocities strongly suggest that the decreasing bounce is caused by the differences in composition and phase of large (diameters greater than 30 nm) and smaller (diameters between 17 and 30 nm) particles.