Differences in the cloud particle material compositions for TiO₂ nucleation (left) and SiO (right). The nucleation species (TiO₂ or SiO molecule) are also surface growth species (as in Table 1 in Helling et al. 2008a). The main differences occur in the uppermost part of the cloud, the haze layer: SiO[s]/MgO[s] with impurities of FeS[s], FeO[s], Fe₂O₃[s], and Al₂O₃[s] in the case of SiO nucleation (right), and MgSiO₃[s]/Mg₂SiO₄[s] with impurities of all other solids plus a very thin TiO₂[s] layer at the very top in the case of TiO₂[s] nucleation (left).