Interactive comment on “Modelling the cloud condensation nucleus activity of organic acids” by Z. Varga et al

The study addresses the ability of various organic acids to act as cloud condensation nuclei. The authors compare effects of water activity (Raoult term) and surface tension (Kelvin term) on the activation behavior for the individual compounds. In order to give a more systematic view on the interpretation of the results, we would like to draw the authors’ attention to our recent model study [Ervens et al., 2005]. Figure 8 of our paper shows that at subsaturated conditions, the saturation (S) is dominated by the Raoult term (B/r3) and only as one approaches saturation does the importance of the Kelvin term (A/r) increase. At the critical supersaturation, the growth factor (wet/dry size) is larger than shown in Figure 1, and, thus, any effects by surface active compounds are negligible (< 10% compared to the surface tension of water which translates into an