Synthetic transmission spectra of GJ 3470b in terms of apparent planetary radius, which are computed for all the 16 models of our grid and the standard model. Each colour corresponds to a set of metallicity and thermal profile. A colour gradient is then used to differentiate the eddy diffusion coefficients and stellar UV fluxes (see legend in the top panel and meaning of each symbol in Table 2). The standard values are shown in Figs. 2 and 3. The standard metallicity is 10× solar (ζ = 10). Observational data points (references in the legend) have also been plotted for comparison.