Vertically integrated CO₂ column density as a function of radius. The solid lines show the total model column density, and the dashed lines show the model column density integrated up to the dust τ = 1 surface at 15 μm. The green and purple crosses represent the retrieved N and R for ¹²CO₂ and ¹³CO₂. The left panel depicts the model using the chemical network, and the right panel depicts the model with parameterized abundances.