Upper panel: density profiles of H (blue) and H₂ (green) and gas temperature profile (red) in the PDR (P = 10⁷ K cm^-3, χ = 10³). Lower panel: local emissivity profiles (color lines) of the first rotational lines of H₂ (solid lines for para transitions and dashed lines for ortho transitions) compared to the local OPR profile (black). Local emissivities are multiplied by d so that the contribution of a given region to the total intensity is proportional to its area under the curve despite the logarithmic axis. Each emissivity curve has been scaled so that its maximum is 1 for ease of comparison.