During the Deepwater Horizon (DWH) blowout, photooxidation of surface oil led to the formation of persistent photooxidized compounds, still found in shoreline sediments a decade later. Studies demonstrated that photooxidation modified both biodegradation rates of the surface oil and the effectiveness of aerial dispersant applications. Despite the significant consequences of this weathering pathway, the lack of measurements prevented photooxidation to be accounted for in the DWH oil budget calculations and in most predictive models. Here we develop a Lagrangian photooxidation module that estimates the dose of solar radiation individual oil droplets receive while moving in the ocean, quantifies the likelihood of photooxidative changes, and continues to track the transport of these persistent photooxidized compounds. We estimate and track the likelihood of photooxidation of Lagrangian oil droplets in the upper layers of the water column for the DWH case by coupling the net shortwave radiation from NOGAPS to the oil application of the Connectivity Modeling System (oil-CMS). The dose of solar radiation upon a droplet is computed with the intensity of the incoming irradiance at the ocean’s surface, the light attenuation coefficient, and the depth of the oil droplets. Considering a range of DWH empirical irradiance thresholds, we find that photooxidation can happen at short time scales of hours to days, in agreement with the new paradigm of oil photooxidation. Furthermore, the oxidized compounds are likely to form in a 110 km radius around the response site, suggesting that the oil reaching the coastline was already photooxidized. This new dynamic coupling provides a powerful tool to test oil weathering hypotheses, refine the oil budget during the DWH, and ultimately inform rapid response in future oil spills.

在深水地平线（DWH）井喷期间，地表油的光氧化作用导致了持久性光氧化化合物的形成，十年后仍在海岸线沉积物中发现了这种化合物。研究表明，光氧化作用既可以改变表面油的生物降解速度，又可以改善空中分散剂的应用效果。尽管这种风化途径会产生重大后果，但缺乏测量方法仍无法在DWH石油预算计算和大多数预测模型中解释光氧化作用。在这里，我们开发了一个拉格朗日光氧化模块，该模块可估算单个油滴在海洋中移动时收到的太阳辐射的剂量，量化光氧化变化的可能性，并继续跟踪这些持久性光氧化化合物的运输。通过将NOGAPS的净短波辐射耦合到连通性建模系统（oil-CMS）的石油应用中，我们估计和跟踪了DWH情况下水柱上层中拉格朗日油滴发生光氧化的可能性。利用海洋表面入射辐照强度，光衰减系数和油滴深度来计算水滴上太阳辐射的剂量。考虑到DWH的经验辐照阈值范围，我们发现光氧化可以在数小时至数天的短时间范围内发生，这与石油光氧化的新范式一致。此外，氧化的化合物很可能在响应点周围110公里的半径内形成，这表明到达海岸线的油已经被光氧化了。