Comparison of the considered broadening mechanisms along a (p_gas, T_gas) profile. All broadening mechanisms are evaluated for their potential minimum and maximum contribution. Thermal broadening is weakest for large clusters (N = 15, ‘Thermal, min’) and strongest for small clusters (N = 1, ‘Thermal, max’). Collisional broadening is weakest for small clusters at high frequencies (N = 1, λ = 10 µm, ‘Collisional, min’) and strongest for large clusters at low frequencies (N = 15, λ = 100 µm, ‘Collisional, max’). Rotational broadening is weakest for large clusters (N = 15, ‘Rotational, min’) and strongest for small clusters (N = 1, ‘Rotational, max’). Natural broadening is weakest for long state life-times at high frequency (τ = 1µs, λ = 10 µm, ‘Natural, min’) and strongest for short state life-times at low frequency (τ = 1ns, λ = 100 µm, ‘Natural, max’). The T(p) profile is one of the WASP-96b-like profiles from Sect. 2.3.