海洋中天然有机物对PAHs的光降解作用机理研究

光化学氧化是海洋石油污染物的主要风化途径之一。天然溶解有机质（DOM）在光化学过程中可通过光敏化作用促进污染物降解，亦可通过光屏蔽等作用抑制降解。目前对DOM影响海洋中多环芳烃（PAHs，典型石油污染物）光化学过程的研究较少，且对DOM的抑制作用及机理的研究仍有待深入。本课题以此为核心问题，将DOM各组分按极性和分子量分别提取，并测试其对PAHs光降解的影响。研究中，结合活性物种稳态浓度测定、活性物种与PAHs的二级反应速率常数测定、PAHs的光降解路径分析以及DFT模拟计算，明确各活性物种对PAHs降解的贡献率；并结合对DOM的表征，揭示DOM促进PAHs光降解的作用机理。另一方面，通过测定DOM的光屏蔽效应、对活性物种的淬灭作用、与PAHs结合的DOM对活性物种的屏蔽效应，揭示DOM对光降解的抑制作用机理。本研究成果有助于更好地理解并预测石油类污染物在海洋中的光化学降解和归趋。

Photochemical oxidation has been considered as a major weathering process for oil contaminants in the ocean. The natural dissolved organic matter (DOM) can promote the photodegradation of organic contaminants via photo-sensitization effect, or inhibit the photodegradation via light attenuation or other effects. However, the investigation of DOM on the photodegradation of polycyclic aromatic hydrocarbons (PAHs, typical petroleum contaminants) in the ocean is limited, and the inhibiting effects of DOM still need to be clarified. In this project, we proposed a strategy to reveal the effects of DOM on the photodegradation of PAHs and their mechanism. During this study, we will analyze the steady state concentration of reactive species during photodegradation process in the presence of DOM, the second-order reaction rate constants between reactive species and PAHs, and the photodegradation pathways of PAHs. Combining with DFT calculation, the contribution of reactive species on the PAHs photodegradation will be obtained. Moreover, based on the characterization of DOM structures and properties, and with the above described experimental results, the underlying mechanism of DOM on accelerating photodegradation rates of PAHs will be revealed. To unveil the inhibition effects DOM on the photodegradation of PAHs, the light attenuation effects of DOM, the reactive species quenching effects of DOM, and the shielding effects caused by complexation of PAHs and DOM will be studied. The results from this project will be beneficial for understanding and predicting the photochemical transformation of petroleum contaminants in the ocean.