Abstract

Petroleum fuels such as kerosene and diesel are important forensic indicators in investigations of fires, explosions, and oil spill incidents. However, environmental exposure can alter their chemical composition through weathering, particularly evaporation, complicating mixture identification and source tracking. In this study, we quantified the unresolved complex mixture (UCM) region in gas chromatography (GC) chromatograms to describe compositional changes in kerosene–diesel mixtures during short-term evaporative weathering and to assess its utility for mixture identification. Artificially contaminated soil samples with various mixing ratios were prepared and subjected to controlled evaporation for up to 90 days. Samples were collected at regular intervals, and the area and distribution characteristics of the UCM region were compared. The results showed that kerosene components evaporated faster than diesel components, and over time the mixtures could appear as a single fuel type when interpreted primarily from major peaks. In contrast, UCM distribution features and area-based indicators differed with the initial mixing ratio, suggesting that UCM analysis can provide clues to mixture presence and initial composition even when peak-based interpretation is ambiguous. Overall, UCMbased GC profiling may complement conventional compound- and peak-centered interpretation and provides foundational data for future validation under broader conditions.