Molar fraction profiles in the troposphere of Uranus obtained with the model of Venot et al. (2012), targeting the 2.1 × 10^-9 upper limit on the upper tropospheric CO mole fraction obtained by Teanby & Irwin (2013). The temperature profile in the troposphere is shown with a solid black line. Thermochemical equilibrium profiles are plotted in black with the same layout as their corresponding species. CO and CO₂ are quenched around 2−3 × 10⁶ mbar. H₂O departs from thermochemical equilibrium because of condensation and causes an increase of other species mole fractions (the sum of all mole fractions is normalized to unity at all levels). The model parameters are: O/H  =  501⊙, C/H  =  18⊙, and K_zz = 10⁸  cm² s^-1.