Effect of the depletion of oxygen and enrichment of carbon to enhance the C/O ratio on the integrated line flux of CO (4.936–5.298 µm) and H₂O (4.891–18.474 µm) and C₂H₂ (11.664–17.289 µm). The circles and triangles represent models where oxygen was depleted and carbon was enriched, respectively, to attain a high C/O elemental ratio. The solid horizontal brown line depicts the integrated C₂H₂ flux. The solid black line denotes the integrated observed line flux of CO, and the dotted vertical line shows the model with a typical C/O ratio of 0.45 similar to Fig. 7.