Molecular column densities (left) and abundances relative to H₂ (right) in foreground clouds along the sight-lines to W49N (blue), W31C (red), G34.3+0.1 (magenta) and G29.96–0.02 (black). The H₂ column densities are derived from CH column densities presented by Godard et al. (2012), for an assumed CH/H₂ ratio of 3.5 × 10^-8 (Sheffer et al. 2008). The error bars are dominated by uncertainties in the CH to H₂ conversion, except for the SO values toward G34.3+0.1. Dashed curves indicate the regions spanned by the range of abundances measured in this set of foreground clouds, with the dotted curve plotted midway between the dashed curves.