Temporal evolution of abundances for CH₄, NH₃, CO₂, and H₂O at different temperature and pressure conditions, as labeled in each figure. Abundances are calculated with the full chemical scheme (red solid lines) and with the reduced scheme (blue dot-dashed lines). These abundances are compared with the thermochemical equilibrium value (black dotted lines). Initial conditions are solar abundances spread into H₂, He, CH₄, O(³P), and N₂.