1. Titan's photochemical model: neutral species L.M. Lara IAA-CSIC Granada, Spain

2. The model (which physico-chemical phenomena are explicitely handled ?) ● Turbulent diffusion – K(z). ● Molecular diffusion. ● Absorption of UV radiation (<278 nm) by aerosols. ● GCR to dissociate N2. ● Deposition of H2O from meteoritic ablation. ● Condensation as growth mass rate of the existing aerosol. ● 17 photodissociation processes and 114 chemical reactions.

3. The equations

4. The discretization scheme (which kind of grid and limit conditions ?) ● Equations solved in height (z) every 6 km, which is about 5 steps per atmospheric scale height. ● Upper boundary condition: zero flux for all species, except H, H2, O(3P) and N(4S) allowed to escape with Jeans' thermal velocity. ● Lower boundary: 1) mixing ratio of condensible species fixed by their saturation law (i.e. no supersaturation). 2) Mixing ratios of non- condensible, long-lived species fixed by observed values. 3) Local photochemical equilibrium for the rest of species in the model affected by transport phenomena, that is CH3, H, N(4S) and O(3P).

5. The algorithms (which solver, convergence levels... ?) ● Equations transformed into finite difference equations, giving rise to a three-diagonal system of equations to be solved by the Crank-Nicholson method ● Convergence is set to 0.01% for every component at every atmospheric level.