1Department of Physics, University of Helsinki, P.O. Box 48, 00014 Helsinki, Finland
2Finnish Meteorological Institute, 00560 Helsinki, Finland
3Department of Applied Environmental Science, Stockholm University, 10691 Stockholm, Sweden
4Department of Physics and Mathematics, University of Eastern Finland, 70211 Kuopio, Finland
5Finnish Meteorological Institute, 70211 Kuopio, Finland
Abstract. Different methods of determining formation rates of 3 nm particles are compared, basing on analysis of simulated data, but the results are valid for analyses of experimental particle size distribution data as well. The study shows that the method of determining formation rates indirectly from measured number concentration data of 3–6 nm particles is generally in good agreement with the theoretical calculation with a systematic error of 0–20%. While this is often accurate enough, a simple modification to the approximative equation for the formation rate is recommended. Additionally, the temporal connection between the concentration of the nucleating vapour and the formation rate is studied. It is concluded that the often used power-law connecting these two is inaccurate.