`The utility of gas chromatography with infrared spectrometric detection (GC-IR) for the structural elucidation of pyrolysate constituents obtained by Flash Vacuum Pyrolysis (FVP; 900-1100 degrees C, 10(-2) Torr) of ethynylated Polycyclic Aromatic Hydrocarbons (E-PAH) is demonstrated. E-PAH are efficient precursors for ubiquitous and genotoxic C14H8, C16H10 and C20H12 cyclopenta-fused PAH (CP-PAH) combustion effluents. The formation of CP-PAH from E-PAH as well as CP-PAH rearrangements and/or interconversions are readily recognized. GC-IR being complementary to GC-MS enables the identification and structural assignment of previously undetected isomeric PAH, which are only present in trace-level amounts. The results are of interest for the elucidation of PAH build up processes and for the rationalization of the ubiquitous formation of a distinct set of PAH during combustion.