Various transit spectra computed with PSG for the three innermost planets of the TRAPPIST-1 system calculated from 3D GCM simulations (assuming H₂O-dominated composition, and also CO₂-dominated for comparison). In the upper panel a, transit spectra of TRAPPIST-1b for various compositions and pressures are compared; in the lower panel b, transit spectra of TRAPPIST-1b, c, and d for two compositions only (10 bar H₂O + 1 bar N₂; 10 bar CO₂) are compared. The dashed lines indicate H₂O cloud-free atmospheres, while solid lines assume H₂O cloudy atmospheres. The dotted lines indicate CO₂ atmospheres (including the effect of CO₂ ice clouds, although extremely limited here; instead, CO₂ condensation was cut off for TRAPPIST-1b and c simulations with 100 mbar of CO₂ as this would cause the atmosphere to collapse on the nightside.). These are relative transit depths; the curves are shifted with arbitrary offsets to compare them more easily.