Molecular column densities toward 5 positions in NGC 7538 S and 2 positions in IRS1. Colored solid lines show the variation for each isotopologue calculated with the optically thin assumption (arrows highlight the upper and lower limits), while dashed lines (OCS_τ, SO_τ, CH₃CN_τ, ¹²CO_τ) show the variation calculated with opacity correction from Eq. (B.10). The uncertainties at each position are determined from T_rot, partition function Q(T_rot), Gaussian fit to , or the scatter of the multi-transitions on the rotation diagrames (CH₃CN and HNCO). For species (e.g. HNCO, SO₂) we have not measured the optical depths, the column densities could be underestimated by a factor of 5−10.