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

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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.