Observational data points are the same as in Figs. 1 to 6. The pink dashed areas show all the values of the dust observables that can be produced by the valid dust models presented in Sects. 3 and 4, i.e. all dust population combinations except 100% FeS nano-inclusions, silicates with 15 and 20 nm thick aromatic-rich carbon mantles, and aliphatic-rich carbon grains without mantles. For models with increased carbon abundances (see Sect. 4.3), we included only those with N_H< 10²⁰ H/cm². Also plotted are models with a decreased carbon abundance. The radiation field is varied with . We further include models for which dust is illuminated by harder radiation fields than the standard ISRF (Sect. 3, for black-bodies at 20 000, 30 000, and 40 000 K and G₀ = 1, 1.5, 2, 2.5, and 3). See Sect. 2.2 for description of the black and white lines and symbols.