Spectral energy distribution (SED) calculated with DustEM for coagulated grains (solid lines): a) 1 BG plus 1000 VSGs, b) 4 BGs plus in total 4000 VSGs (two components) and c) 4 BGs plus in total 4000 VSGs (one component). The dashed lines indicated the calculated SED of the diffuse ISM determined with DustEM for single grains as in Fig. 1 before coagulation (dashed lines). The symbols indicate the observations of the diffuse ISM as shown in Fig. 1; “car” indicates amorphous carbon and “sil” indicates astronomical silicate, “mixed” indicates aggregates with 4 BGs, where 1 BG is of amorphous carbon and 3 BGs of astronomical silicate, and of 16 BGs, where 4 BGs are of amorphous carbon and 12 BGs of astronomical silicate.