Molecular column densities (panels in the left column) and abundances (panels in the right column) towards 8 positions in Orion-KL. The molecular abundances of each species with respect to H₂ are converted from C¹⁸O, assuming a constant N_C¹⁸O/N_H2 ~ 1.79 × 10^-7 ratio. Column densities and abundances with the uncertainties are measured as mentioned in Sect. 4.4 and Tables A.5−A.7. Coloured solid lines show the differentiation for each isotopologue calculated from optically thin assumption (arrows highlight the upper limits), while dashed lines show the differentiation calculated with optical depth correction from Eq. (10). For abundant molecules (e.g., HNCO, SO, SO₂, CH₃OH) which we have not measured their line optical depths, their densities could be underestimated by a factor of 7−10.