Thermodynamic behavior of stable carbon isotopic compositions of individual polycyclic aromatic hydrocarbons derived from automobiles

Tomoaki Okuda, Hideshige Takada, Hiroshi Naraoka

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19 Citations (Scopus)


Concentrations, molecular compositions, and compound-specific stable carbon isotopic compositions (δ13C) of polycyclic aromatic hydrocarbons (PAHs) in gasoline exhaust particles (GEPs) and diesel exhaust particles (DEPs) were investigated in this study. δ13C of PAHs in GEPs ranged from -13.3‰ to -26.8‰, and that in DEPs ranged from -21.7‰ to -26.3‰. The interspecies δ13C variations in each sample were 5.3 ± 2.2‰ in GEPs and 2.6 ± 1.3‰ in DEPs. PAHs in GEPs show larger interspecies δ13C variation than those in DEPs; hence, a degree of carbon isotopic fractionation during the conversion from fuel to PAH seems to be larger in gasoline engines than that in diesel engines. Pyrene series PAHs, which consist of only hexagonal rings, in almost all GEP samples show strong negative correlation between the H/C ratio and δ13C whereas fluoranthene series PAHs, which contain a pentagonal ring, show less systematic isotopic behavior in GEP samples. A kinetic isotope effect in thermal cracking of organic macromolecules may be minor for PAH formation in vehicle engines. We suggest that the isotopic trend of pyrene series in GEPs can be explained by a thermodynamic isotope effect, and that disturbance from isotopic equilibrium may cause a weak correlation between the isotopic behavior and the H/C ratio among the interspecies PAHs.

Original languageEnglish
Pages (from-to)219-236
Number of pages18
JournalPolycyclic Aromatic Compounds
Issue number2
Publication statusPublished - 2003 Jun 24



  • Automotive exhaust particles
  • Carbon isotope analysis
  • Compound-specific δC
  • Formation mechanisms
  • Polycyclic aromatic hydrocarbon (PAH)
  • Thermodynamic isotope effect

ASJC Scopus subject areas

  • Polymers and Plastics
  • Organic Chemistry
  • Materials Chemistry

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