Main beam brightness temperature spectra of ¹²CO 3 → 2 (black) and ¹³CO 1→0 (red) emission in the velocity range 55 to 95 km s^-1 and temperature range −0.2 to 12 K. The area corresponds to the centre region of the IRDC G28.37+0.07, outlined in Fig. 8. The dust column density from Herschel is overlaid as blue contours (levels 4,5,7,10,16 × 10²² cm^-2), and the numbering from 1 to 6 indicates the position of submm-continuum sources labelled using ATLASGAL and subsequently observed in N₂H⁺ (Tackenberg et al. 2014).