Biogeochemical processes and Air-sea exchange in the Sea-Surface microlayer (BASS): Chemical and photochemical transformation of organic matter

海面微层(SML)是海洋表面普遍存在的一种特征，其厚度通常为1 mm，构成了大气和海洋之间的边界层。直接暴露于紫外线辐射和大气中的氧化性物质，以及光敏剂和反应物浓度与底层散装水相比增加，都会引发特定于SML的反应。然而，它们在整个有机质转化或挥发性有机化合物排放到大气中的作用，以及它们在海-气相互作用模式中的实施，到目前为止都没有得到足够的限制或了解。在这个项目中，我们将与研究单位“海表面微层中的生物地球化学过程和海-气交换”中的其他跨学科项目提案密切相关，我们将讨论非生物SML特有的光化学、非均相氧化和自由基驱动反应的分子细节。我们的目标是定量描述界面产物的形成，并更好地量化基础散装水和SML之间在化学转化率、周转和选择性方面的差异。结合三个研究小组的专业知识，先进的光化学、基于激光的动力学和光谱、分析和分子建模技术将结合在一起，以提高我们在复杂的海洋SML反应环境中对此类过程的分子水平和机理的理解。特别是，计划中的研究受益于各种方法，包括最先进的振动和频谱学、超性能液相色谱质谱、激光闪光光解-激光长程吸收，以及分子动力学模拟和量子化学计算。计划中的工作包侧重于SML整体和单层代用品的氧化动力学(例如，卤素/羟基自由基反应、表面活性脂肪酸的臭氧分解)、SML代用品与天然和模型光敏剂的光化学反应能力(例如，增强自由基形成和有机单层分解)，以及环境样品的分析(例如，通过靶向表面活性剂的形成和光解产物在水华事件中)。所有这一切将得到方法开发的补充，包括用于有机化合物(例如，羰基和碳水化合物)定量分析的改进的测量方案，开发表面活性光敏剂(例如，苯甲酰苯甲酸衍生的脂类)，以及根据需要实施多水平模拟方案，以全面从理论上了解脂肪酸臭氧化反应的结构-活性趋势(例如，通过考虑有机基质的空间和电子效应来计算速率常数)。

The sea-surface microlayer (SML), a ubiquitous feature of the ocean surface with usually < 1mm thickness, forms the boundary layer between atmosphere and ocean. Direct exposure to UV radiation and to oxidizing species from the atmosphere as well as the increased concentrations of photosensitizers and reactants compared to the underlying bulk water trigger SML-specific reactions. However, neither their roles in overall organic matter transformation or emission of volatile organic compounds to the atmosphere nor their implementation in air-sea interaction models are sufficiently well constrained or understood until now. In this project, which will be closely interlinked with other interdisciplinary project proposals within the research unit “Biogeochemical processes and Air-sea exchange in the Sea-Surface microlayer (BASS)”, we will address molecular details of abiotic SML-specific photochemical, heterogeneous oxidation, and radical-driven reactions. We aim to quantitatively describe the interfacial product formation and to better quantify differences in chemical conversion turnover and selectivity between underlying bulk water and SML. Combining the expertise of three research groups, advanced photochemical, laser-based kinetic and spectroscopic, analytical, and molecular modeling techniques will be combined to improve our molecular-level and mechanistic understanding of such processes in the complex marine SML reaction environment. In particular, the planned research benefits from a wide variety of methods, including state-of-the art vibrational sum-frequency spectroscopy, ultra-performance liquid chromatography mass spectrometry, laser flash photolysis-laser long path absorption, as well as molecular dynamics simulations and quantum-chemistry calculations. Planned work packages focus on the oxidation kinetics of SML bulk and monolayer proxies (e.g., halogen/hydroxyl radical reactions, ozonolysis of surface-active fatty acids), the photochemical reactivity of SML proxies with natural and model photosensitizers (e.g., enhanced radical formation and organic monolayer decomposition), and the analysis of ambient samples (e.g., by targeting surfactant formation and photolysis products during a bloom event). All this will be complemented by method developments, comprising refined measurement protocols for quantitative analysis of organic compounds (e.g., carbonyls and carbohydrates), the development of surface-active photosensitizers (e.g., benzoylbenzoic acid derived lipids), and the implementation of multilevel modeling schemes as needed to get a full theoretical understanding of structure-reactivity trends of fatty acid ozonolysis (e.g., calculation of rate constants by considering steric and electronic effects of the organic matrix).