Gas-phase C/H ratio (normalised by the ratio at t₀) as a function of distance from a solar-mass star for a disc characterised by α = 10⁻³. Blue lines represent a standard model that excludes the thermal decom-position of refractory organics (e.g. Mah et al. 2023), while red lines show the results from our model including that effect. The sublimation lines of the main species contributing to the C/O ratio are indicated with vertical lines. From this plot, we see that the thermal decomposition of refractory organics redistributes gaseous carbon-bearing species through the disc, and hence it significantly influences the gas-phase C/H ratio.