Chemical dispersants are one of many tools used to mitigate the overall environmental impact of oil spills. In principle, dispersants break up floating oil into small droplets that disperse into the water column where they are subject to multiple fate and transport processes. The effectiveness of dispersants typically decreases as oil weathers in the environment. This decrease in effectiveness is often attributed to evaporation and emulsification, with the contribution of photochemical weathering assumed to be negligible. Here, we aim to test this assumption using Macondo well oil released during the Deepwater Horizon spill as a case study. Our results indicate that the effects of photochemical weathering on Deepwater Horizon oil properties and dispersant effectiveness can greatly outweigh the effects of evaporative weathering. The decrease in dispersant effectiveness after light exposure was principally driven by the decreased solubility of photo-oxidized crude oil residues in the solvent system that comprises COREXIT EC9500A. Kinetic modeling combined with geospatial analysis demonstrated that a considerable fraction of aerial applications targeting Deepwater Horizon surface oil had low dispersant effectiveness. Collectively, the results of this study challenge the paradigm that photochemical weathering has a negligible impact on the effectiveness of oil spill response and provide critical insights into the “window of opportunity” to apply chemical dispersants in response to oil spills in sunlit waters.

中文翻译：

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光化学氧化降低了应对“深水地平线”泄漏事故而应用的空气分散剂的功效。

化学分散剂是许多用于减轻溢油对环境整体影响的工具之一。原则上，分散剂将漂浮的油分解成小滴，然后分散到水柱中，在水柱中它们会受到多种命运和运输过程的影响。分散剂的有效性通常随着环境中石油的老化而降低。有效性的下降通常归因于蒸发和乳化，而光化学风化的贡献被认为是微不足道的。在这里，我们旨在使用“深水地平线”溢油过程中释放的Macondo井油作为案例研究来检验该假设。我们的结果表明，光化学风化对深水地平线的影响油的性质和分散剂的有效性可以大大超过蒸发风化的影响。曝光后分散剂效果的下降主要是由于光氧化原油残渣在包含COREXIT EC9500A的溶剂系统中的溶解度降低所致。动力学建模与地理空间分析相结合表明，针对Deepwater Horizo​​n地表油的航空应用中，相当一部分具有较低的分散效果。总的来说，这项研究的结果挑战了光化学风化对溢油应急反应的影响可忽略不计的范式，并提供了对“机会之窗”应用化学分散剂应对阳光照射下的溢油的“机会之窗”的重要见解。