Simulated SED contributions of the smooth-disc model (left) and the PAH-gap model (right) seen in a face-on view. The PAH features are dominated by neutral emission, as expected (Maaskant et al. 2014). While the smooth-disc model emission mainly comes from gas-phase PAHs, the PAH-gap model has a significant contribution from the adsorbed PAHs that dominate the longer-wavelength features. The integrated PAH emission in both models does not scale with the total number of PAHs in the disc because five times more PAH flux is missing than in PAH molecules.