Opacity laws from Ossenkopf & Henning (1994): black dashed line – uncoagulated thin ice mantle dust model; black solid line – thin ice mantle model after coagulation for 10⁵ y at density of n(H) = 10⁶ cm^-3; and from Weingartner & Draine (2001): red lines, models for R_V = 3.1, R_V = 5.5 and R_V = 5.5 “case B” shown with solid, dashed, and dotted lines. The figure also shows the adopted 8 μm opacity (diamond) and the effective opacities corresponding to the empirical conversion of NIR extinction to mass surface density (symbols detailed in the panel), see Sect. 2.2.