Panel a: absorption (σ_abs, upper panel) and scattering (σ_sca cross sections, lower panel). In each panel, PAH, VSG and BG are shown in blue, light blue and green, respectively. The gray curve shows the total absorption. We assume f_PAH = f_PAH, 0 = 4.57%. The mass fraction of BG and VSG (given in the left panel) are then deduced using the random-walk technique. Panel b: extinction (τ_λ) curves normalized to the FUV band. We compare those extinction curves to observational measurements: Mathis et al. (1983) Milky Way (dashed black line) and Gordon et al. (2003) for SMC (gold solid line), LMC (orange solid line) and Milky Way (red solid line). Lower panel: Albedo (ω_λ). In the two panels, the color of the curves is linked to the PAH fraction assumed, from 10⁻² × f_PAH, 0 (blue) to 10 × f_PAH, 0 (green).