Resulting chemical concentrations ϵ_i = n_i/n_〈H〉 of selected molecules in the PRODIMO disc model for EX Lupi. Additional contour lines are plotted as boundaries, including the ionisation parameter χ/n_〈H〉 (i.e. the UV field strength divided by the hydrogen nuclei particle density) and the ratios of the concentrations of the major molecules. For example, ‘H/H2=100’ means that H atoms are 100 times more abundant than H₂ molecules.