Study of the effects of weathering on the chemical composition of a light crude oil using GC/MS GC/FID

Quantitative information on the weathering of spilled oil is essential to a fuller understanding of the fate and behavior of oil in the environment. Such data is also useful for spill modeling. The key to acquiring data on oil weathering is the availability of precise and reliable chemical information. Exact quantitation of compounds in the oil can provide this crucial data. In this study, the effects of weathering on the chemical composition of a light crude oil, Alberta Sweet Mix Blend (ASMB), were thoroughly investigated using GC/FID and GC/MS. Complete compositional information on the ASMB oil at various degrees of evaporation (0-45%) was obtained, and the composition and concentration changes of key components and component groupings were quantitatively correlated to evaporative loss. Two opposing effects during evaporation-one is the loss of oil components due to evaporation, and another is build-up of oil components due to volume deduction-were examined. So-called ''pattern recognition'' plots involving more than 100 important individual oil components and component groupings were graphically depicted, and these permitted deduction of a best set of values for quantitation of exposure to evaporative weathering. A ''weathering index'' concept is proposed. Relatively simple and very useful mathematical equations were derived which can be utilized to describe the weathering behavior of oil and to estimate the evaporation extent of oil. (C) 1995 John Wiley & Sons, Inc.