Emission intensity ratio (I_11.2/I_3.3) vs. the number of carbon atoms (N_C). Circles represent the full dataset of 15 022 neutral PAHs. Squares denote the subset of 81 species selected by Maragkoudakis et al. (2020), characterized by N_C > 20, the presence of solo C–H bonds, and the absence of heteroatoms. All spectra were re-computed using a 6 eV cascade model. The lines depict the fit where R² values highlight the fitting quality.