Disk structure and line contribution functions (CBFs) for the TW Hya model with Δ_{gas / dust} = 200 and [C]/[H]_gas = 10^-6 (depleted). The CBF panels show the abundance (colour fill) and line emission (black lines) of CO, [C i], C₂H, [C ii], and HD. The black contours encompass 25 and 75% cumulative contributions to the line emission. The solid and dashed white lines show the τ = 1 surface for the line and continuum emission. The solid white lines for T_gas and T_dust are the 20 and 50 K isotherms.