Left: transmission spectra of Wasp-121b at a resolution of R = 100 for GCM simulations assuming a constant H₂ abundance in the whole atmosphere. When water dissociation is taken into account (light blue line), the water features become shallower compared to when no water dissociation is assumed (blue line). Right: transmission spectra of Wasp-121b at a resolution of R = 100 for GCM simulations taking into account H₂O dissociation in the atmosphere. When H₂ dissociation is considered (blue line), the CO features appear more clearly compared to when we neglect H₂ dissociation (light blue line). The black and gray curve correspond to the transmission spectra for an atmosphere without CO for the water constant and the dissociated case, respectively, to highlight the features of CO in the other curves.