The classical hydrates interaction model and the classical condensation model have been compared in the temperature range 153.15–363.15 K. Various expressions for the kinetic part of nucleation rate have been examined. In the present study the saturation vapor pressure values of sulfuric acid given by Ayers et al. are extrapolated to lower (stratospheric) temperatures taking into account the temperature dependence of the enthalpy of vaporization. In our model calculations we have compared the effect of three different expressions for saturation vapor pressures. The nucleation rate will differ by several orders of magnitude (depending on temperature, water and acid activity) when using different theories and/or saturation vapor pressures.