Reddening of the background QSOs with detected C i absorption versus N(H i) of the C i absorbers. Symbol conventions are the same as in Fig. 10. The solid curve shows the relation observed in the local ISM where E(B−V) /N(H)= 1.63 × 10^-22 mag atoms^-1 cm² (Gudennavar et al. 2012). The dotted curve illustrates a reddening per hydrogen atom ten times higher than that. The dashed curves correspond to the observations of the Magellanic Clouds (Gordon et al. 2003). The long-dashed curve shows the relation derived for typical DLAs at z_abs ≈ 2.8 (e.g., Vladilo et al. 2008; Khare et al. 2012).