Transmission spectra of Wasp-121b at resolution R = 100 for an atmosphere composed of He, H₂, H₂O, CO, TiO, VO, Na, and H⁻ using the analytical fit for the thermal dissociation of the species in Parmentier et al. (2018; blue). Shown is a comparison of the models with HST/WFC3 data taken from Evans et al. (2016; black dot) and with two models from Parmentier et al. (2018), the first without clouds (magenta) and the second with CaTiO3 clouds (green).