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, at least within the accuracy of the applied model. 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 accuracy is often enough, a simple modification to the approximative equation for the formation rate is recommended. A brief study on real atmospheric data implied that in some cases the accuracy gain may be significant.