Integrating manufacturing era estimation and source identification of diesel spills in Taiwan: Leveraging hydrodesulfurization (HDS) markers and regulatory history

Diesel spill samples from contaminated soils at 12 gas stations operated by two major petrochemical companies in Taiwan were analyzed for manufacturing era estimation and source identification. To address the analytical challenges in dating weathered middle distillate fuels, this study established an integrated environmental forensic framework. Both the spilled samples and 12 Ultra-Low Sulfur Diesel ( ULSD ) reference samples collected between 2018 and 2025 were analyzed by gas chromatography/mass spectrometry (GC/MS). Diagnostic ratios (DRs) of linear alkanes, isoprenoids, bicyclic sesquiterpanes, polycyclic aromatic hydrocarbons (PAHs; including naphthalenes, phenanthrenes, benzothiophenes), as well as hydrodesulfurization ( HDS ) products (biphenyls, tetralins, and indanes), were quantified using the conserved stable C 15 sesquiterpane derivative (BS3) as an internal reference denominator. Principal Component Analysis (PCA) of fingerprint ratios for phytane (Ph), dimethylbiphenyls (C 2 B), trimethyltetralins (C 3 T), and the sesquiterpane BS4 effectively separated samples into distinct clusters corresponding to their respective manufacturers. Supervised Linear Discriminant Analysis (LDA) further classified samples according to historical sulfur regulation periods, as inferred from dibenzothiophenes (C x D, x = 1 and 2). The use of technology-driven markers, such as C 2 B, C 3 T, and trimethylnaphthalenes (C 3 N), enabled the assignment of samples to specific regulatory eras. For instance, the oldest spills were traced back to the proposed pre-1997 era (> 1,500 ppm sulfur content), while recent spills were linked to the 2002−2011 regulatory period. Overall, the application of novel HDS product ratios within a multivariate statistical framework provides a robust forensic methodology that is directly aligned with the country’s regulatory history over the past thirty years.