Trends of CO₂ (top) and H₂O (middle) vapour masses (left) and column densities (right) and their ratio (bottom) with R_gap at different stages of evolution for discs with traffic jams inside the water snow line (Scenario 1). The initial condition is in grey, while increasingly dark shades of green correspond to increasingly late times. The model with R_gap = 1 au is plotted separately at the dots as its gap is located very close to the H₂O snow line and thus inside the CO₂ snow line. A smooth disc model is included for comparison as the triangles. Equations (23) (dashed-dotted) and (11) (dotted) are plotted as guides to the eye the trends for approximate trends at early and late times.