Influence of the evaporation of the different chemical species on the dust-to-gas ratio in the protoplanetary disk. Left plot: dust-to-gas ratio in terms of the total dust-to-gas ratio in the disk as a function of temperature. After each species evaporates the total mass fraction decreases by the corresponding mass fraction (see Table 1) until all species evaporate beyond 1500 K. Right plot: example of the dust-to-gas ratio as a function of orbital distance for the disk with α = 10⁻³, Σ_g,0 = 2000 g cm⁻², and u_f = 10 m s⁻¹, and a globaldust-to-gas ratio of 1.5%. Overplotted is the temperature of the disk where the evaporation fronts are easy to locate.