Left: difference in modelled zonally averaged spectra when HCN (55^∘S), CO₂ (65^∘S), and H₂O (75^∘S) are added (red) and when they are not present (blue) compared with the observations (black). Right: vertical profiles retrieved for each of the molecules. The black profiles corresponds to the a priori profiles used. The red profiles correspond to the retrieved vertical profile for each spectra.