The parametric T-P profile of the atmosphere of HD 209458 b (thick red solid line), as adjusted over HST/STIS observations by Sing et al. (2008b). The three adjusted (T, P) parameters are shown with their temperature error bars (red). The tripled-dot-dashed line shows the level of Na abundance drop at 3 mbar pressure. The thin solid line shows the 32 mbar pressure measured at the base of the sodium absorption line using the Rayleigh scattering. The dotted line shows the CH₄/CO equilibrium curve. The dashed lines show the condensation curves for sodium, iron, and titanium.