ĸ_R (solid and dashed coloured curves) as a function of pressure for atmospheres with varying and Na and K abundances calculated along a Saturn profile. The abundance of all other heavy elements is eight times solar. The solid curves were computed using the Na D and K I HWHM formulation from Eq. (6), while the dashed curves use the Na D and K I HWHM formulation from Allard et al. (2016), Allard et al. (2019), Allard et al. (2023) and Allard et al. (2024). The dashed black curve corresponds to the critical opacity, ĸ_crit.