Azimuthally averaged radial profiles of the fiducial model at t = 75 751 yr (176 orbits). (a) Radial profile of total gas density (blue), CH₄ ice (green dashed), and CH₄ vapor (green solid) at 176 orbits. The gas phase C/O ratio (black) is calculated based on the abundance assumed in Table 1. (b) The expected C₂H column density based on Eq. (22). The shaded region indicates the one-magnitude uncertainty of the fitting constant F_C in Eq. (22). We mark the typical C₂H peak density (orange) from the MAPS data constraint as a reference value for illustration.