Non-thermal velocity dispersion (σ_NT) vs. gas kinetic temperature derived from the para-H₂CO line ratio (Sect. 3.2) for locations with the Mach number M ≳ 2.5 in the OMC-1 (blue points) and ATLASGAL massive star-forming clumps (green points; Tang et al. 2018). The blue line is the result from a linear fit for the OMC-1 data. The red line is the linearly fitted result for OMC-1 (M ≳ 2.5) and ATLASGAL data. Black solid and dashed lines indicate relations between non-thermal velocity dispersion and gas kinetic temperature derived from para-H₂CO and NH₃ at density 10⁵ cm^-3 in the Galactic CMZ clouds, respectively (Güsten et al. 1985; Immer et al. 2016).