Evolution, as a function of galactic age t, of the following quantities for the Milky Way model: star formation rate ψ(t) (relative to its maximal value); dust mass M_d(t) (idem); ratio of the bolometric luminosity emitted by dust in the whole galaxy, , to the overall bolometric luminosity of the galaxy, ℒ_gal(t); ratio of the bolometric luminosity emitted by dust in star-forming clouds, , to .