Evolution of the ratio between the wavelength-dependent FUV gas absorption coefficient and the dust extinction coefficient (absorption plus scattering) as a function of A_V for two representative continuum wavelengths: one below the C⁰ photoionization threshold (black curve) and one above (red curve). For positions where the black curve is greater than 1, C⁰ photoionization dominates the absorption of FUV photons with λ < 1101 Å. This process reduces the amount of FUV photons that pump the NIR oxygen lines close to the PDR surface.