Left: vertical abundance profiles determined after 1000 runs with the full chemical scheme (grey lines) for H₂O, CH₄, and CO. The nominal results of the full chemical scheme (red lines), thermochemical equilibrium (black lines), and results obtained with the reduced scheme (blue lines) are also shown. Right: corresponding distribution of abundances at 1 mbar represented with grey bars, with nominal abundances of the full scheme (red lines), abundances obtained with the reduced scheme (blue lines), and the 1-σ intervals around the nominal abundances (green dotted lines). Blue and red lines are very close on each plot.