Atmospheric photochemistry at the edge – Following the production of volatile organic compounds at the air water interface with sum frequency generation spectroscopy

海洋、湖泊和河流覆盖了地球表面的70%。水表面覆盖着一层有机分子，称为海面微层(SEA-SML)。SEA-SML由脂类、蛋白质、多糖和碳氢化合物等有机化合物组成，有机分子在水面的高局部浓度促进了太阳光诱导的光化学反应，而在本体溶液中这种光化学反应被抑制。因此，海洋表面代表着一个巨大的催化表面。这些光化学反应产生挥发性有机化合物(VOCs)，有可能对生态系统、区域和全球气候产生巨大影响，因此它们也对人类生活产生重大影响。这些在海洋表面发生的光化学反应的产物和反应途径仍不清楚。已有的实验研究了溶液或气相中的反应产物。缺少的是在空气-水界面的直接方法，即反应实际发生的地方。本项目的重点在于用表面专一性方法研究表面的光化学反应途径及其反应动力学。因此，我将使用总和频率发生光谱(SFG)和飞行时间二次离子质谱仪(ToF-SIMS)进行测量。在这里，重点完全集中在水面上的反应-海-SML。时间分辨SFG光谱-具有ps的时间分辨率-将记录反应动力学。ToF-SIMS的化学特性有助于将SFG光谱的振动特征与化学信息联系起来。更好地理解SEA-SML中的光化学反应将有助于提高对全球生态系统中化学关系的理解。

Oceans, lakes and rivers cover 70% of our planet’s surface. The water surface is covered with a layer of organic molecules which is called Sea-Surface Microlayer (sea-SML). The sea-SML is composed of organic compounds like lipids, proteins, polysaccharides and hydrocarbons.The high local concentration of organic molecules at the water surface promotes sun light induced photochemical reactions, which are inhibited in bulk solutions. Therefore, the ocean surface represents a vast catalytic surface. Those photochemical reactions generate volatile organic compounds (VOCs) which have the potential to be a tremendous impact on ecosystems, regional and global climate and therefore they also have a major impact on human life. The products and reaction pathways of these photochemical reactions at the ocean surface are still unclear. Existing experiments have studied the reaction products either in solution or in gas phase. What is missing is a direct approach at the air-water interface, where the reactions actually take place. The focus of this project lies on studying the photochemical reaction pathways at surfaces and their reaction kinetics with surface specific methods. Thus, I will perform measurements with Sum Frequency Generation spectroscopy (SFG) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Here, the focus lies exclusively on reactions at the water surface - the sea-SML. Time resolved SFG spectroscopy - with a ps temporal resolution - will record the reaction kinetics. The chemical specificity of ToF-SIMS helps to connect the vibrational signatures of SFG spectroscopy to chemical information.A better understanding of the photochemical reactions at the sea-SML will help to improve the understanding of chemical relationships in the global ecosystem.