Diagnostic plots showing the origin of the PAH flux in the disk, i.e. the contributions of PAH emission to the final spectrum. The intensity of the PAH flux is shown in logarithmic scale (arbitrary scaling), where each color spans an order of magnitude. Top left: HD 97048, top right: HD 169142, bottom left: HD 135344 B, bottom right: Oph IRS 48. The red, black and blue solid lines give the locations where the neutral fractions f(0) are respectively 0.25, 0.5, 0.75. The neutral fractions are computed by Eqs. (4) and (5) in each grid cell of the disk. PAHs in the surface of the disk are largely ionized, while PAHs in the mid-plane are neutral. The dashed black line is the vertical τ_MIR = 1 surface at 10 μm, the dash-dotted grey line gives the radial τ_UV = 1 surface at 0.1 μm. The height θ relates to Z by, θ = tan   (Z/r).