Temporal evolution of the abundance of CO (left) and CH₄ (right) at their quenching levels in GJ 436b (top), HD 209458b (middle), and HD 189733b (bottom). The corresponding pressures and temperatures are indicated on each panel. The abundances obtained with the updated chemical scheme (solid red lines) are compared to those obtained with the former scheme of Venot et al. (2012) (dotted blue lines), to the updated chemical scheme to which has been added Hidaka’s reaction (dot-dashed green lines) and to the thermochemical equilibrium at these conditions of P and T (dotted black lines). The initial conditions are the thermochemical abundances (assuming solar elemental abundances) at 1 bar and 1100 K (for GJ 436b), at 3.5 bars and 1750 K (for HD 209458b), and at 13 bars and 1570 K (for HD 189733b).