Chemical Composition and Fingerprints of Headspace Vapors of 37 Petroleum Products and Non-Aqueous Phase Liquid Samples

Abstract

In this study, the headspace vapor compositions of 37 unreleased petroleum products and field-collected non-aqueous phase liquid (NAPL) samples including crude oil, gasoline, diesel, kerosene, jet fuel, naphtha, tar, lubricating oil, and field NAPL were measured using an innovative high-resolution analytical method. Gasoline and some crude oils are highly volatile while diesel, kerosene, and jet fuel have much lower volatility. In unreleased gasoline and some light distillates, benzene, toluene, ethylbenzene, and xylenes (BTEX) constitute the majority of volatile aromatic hydrocarbons. As the BTEX compounds represent only a few of the known compounds in gasoline and light distillate products, monitoring only BTEX concentrations in vapor samples may not be sufficient to distinguish among lighter petroleum products nor to totally assess all toxicity associated risks in lighter fuels, both for unreleased and released weathered products. For crude oil vapor samples, however, we found a characteristic distribution of compound groups and carbon number range distribution despite varying widely in TVOC concentration, allowing clearer specific product identification. In addition, we found that total VOC composition in middle distillate fuel vapor samples was more variable indicating that vapor fingerprinting is less useful for identification of middle distillate fuel sources. Similarly, the ratios of individual VOCs in vapor samples could be used to identify specific gasoline and crude oil NAPL sources but was not applicable to many middle distillate fuel sources. This study provides valuable data on the maximum concentrations that could potentially partition from typical petroleum products into the vapor phase, as well as the compositional benchmarks of VOC vapors from petroleum products and NAPL samples.