Results of the standard model (K = 10⁸ cm² s^-1; ). Panel a: nucleation rate , which follows a log-normal distribution around a reference pressure P_*. The dotted horizontal lines indicate the bottom and top of our computational domain. Panel b: concentrations of nuclei (), condensates (x_c), and vapor (x_v). The equilibrium concentration corresponding to the saturation pressure is also plotted (x_eq) but it virtually coincides with x_v. Panel c: characteristic grain radius a_p. The dashed lines correspond to a model where the nuclei are inserted at a higher layer than the standard. The open circles correspond to the depth where the geometrical transmission optical depth τ_trans equals 1.