Abstract Photooxidation was an important weathering process for spilled oil at the water surface following the Deepwater Horizon oil spill, leading to the rapid formation of polar or oxygenated hydrocarbons, or photo-generated asphaltenes. While the great extent and rapid time scale of this process have been well documented, little is known about the formation pathways and chemical structures of photo-generated asphaltenes. To address this knowledge gap, we conducted a 44-day natural sunlight exposure experiment using Louisiana light sweet crude oil amended in seawater. The saturate, aromatic, resin and asphaltene fractions were separated and quantified by adsorption chromatography. Molecular details were obtained by thermal slicing ramped pyrolysis-gas chromatography–mass spectrometry, while bulk structural changes were quantified by 13C solid-state nuclear magnetic resonance. These analyses illustrate that, in comparison to the “native” petrogenic asphaltenes in crude oil, photo-generated asphaltenes had larger bridged-island structures with smaller aromatic cores and longer alkyl tails in each island. Our results also demonstrated that the large aliphatic fraction of the photo-generated asphaltene was sourced from the alkyl moieties of the aromatic fraction rather than the saturate fraction. A group of intact hydrocarbons, predominantly n-alkanes (C16–C28), was occluded in both native and photo-generated asphaltene matrices. Overall, these results provide insight into the formation mechanisms and structural details of photo-generated asphaltenes in oils after exposure to natural sunlight in Gulf of Mexico waters. This knowledge is valuable for developing remediation strategies for oil spills, in particular those under strong solar irradiance.

中文翻译：

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阐明在墨西哥湾暴露于自然阳光后，轻质路易斯安那低硫原油光生沥青质的形成途径

摘要 光氧化是深水地平线溢油后溢油在水面的重要风化过程，导致极性或含氧碳氢化合物或光生沥青质的快速形成。虽然该过程的范围广且时间快，但对光生沥青质的形成途径和化学结构知之甚少。为了解决这一知识差距，我们使用路易斯安那州在海水中修正的轻质低硫原油进行了 44 天的自然阳光照射实验。通过吸附色谱分离和定量饱和烃、芳香烃、树脂和沥青质馏分。通过热切片梯度热解-气相色谱-质谱法获得分子细节，而整体结构变化则通过 13C 固态核磁共振进行量化。这些分析表明，与原油中的“天然”石油沥青质相比，光生沥青质具有更大的桥岛结构，每个岛的芳香核更小，烷基尾更长。我们的结果还表明，光生沥青质的大部分脂肪族馏分来自芳族馏分的烷基部分，而不是饱和馏分。一组完整的碳氢化合物，主要是正烷烃（C16-C28），被封闭在天然和光生沥青质基质中。总体而言，这些结果提供了对暴露于墨西哥湾水域自然阳光后油中光生沥青质的形成机制和结构细节的深入了解。