Observed and modelled spectra for the methanol transitions with absorption features towards W3(OH). The short line name of each transition is denoted in the lower left corner of each panel. The blue spectra represent the observed data, and the red curves indicate the fitted line from the two-layer model with adopted parameters listed in Table A.5. The vertical black dashed lines represent the systemic velocity of V_LSR = −46.19 km s⁻¹.