Abstract：
Pyruvic acid (PA) is a ubiquitous 2-oxocarboxylic acid in the atmosphere. Its photochemical process at the air-liquid (a-l) interface has been suggested as an important source of aqueous secondary organic aerosols. We investigated the photochemical reaction pathways of PA at the a-l interface using synchrotron-based vacuum ultraviolet single-photon ionization mass spectrometry (VUV SPI-MS) coupled with the System for Analysis at the Liquid Vacuum Interface (SALVI) microreactor. Results from mass spectral analysis and the determination of appearance energies (AEs) indicate that photolysis of PA can generate radicals, then they recombine with carboxylic acids and simple molecular oligomers. Furthermore, the preliminary products could form larger oligomers via radical reaction or esterification in the presence of hydroxyl and carboxyl functional groups. Mass spectral comparison shows that most photochemical reactions would complete within 4 h. The expanded photochemistry-driven reaction flowchart of PA is proposed based on the newly discovered products. Our results reveal that the interfacial PA photochemical reactions have different mechanisms from the bulk liquid due to the interfacial properties, such as molecular density, composition, and ion concentration. Our findings show that in situ mass spectral analysis with bright photon ionization is useful to elucidate the contribution of a-l interfacial reactions leading to aqSOA formation.
摘要：
丙酮酸(PA)是大气中普遍存在的2-氧代羧酸。它在气液（a-l）界面处的光化学过程已被认为是水性二次有机气溶胶的重要来源。我们使用基于同步加速器的真空紫外单光子电离质谱（VUVSPI-MS）和液体真空界面分析系统（SALVI）微反应器，研究了PA在a-l界面的光化学反应途径。质谱分析和外观能（AE）的测定结果表明，PA的光解可以产生自由基，然后它们与羧酸和简单的分子低聚物重组。此外，在羟基和羧基官能团的存在下，初步产物可以通过自由基反应或酯化形成较大的低聚物。质谱比较表明，大多数光化学反应将在4小时内完成。基于新发现的产物，提出了PA的扩展光化学驱动反应流程图。我们的结果表明，由于界面性质，界面PA光化学反应具有不同于本体液体的机理，例如分子密度，composition,和离子浓度。我们的发现表明，具有亮光子电离的原位质谱分析可用于阐明a-l界面反应导致aqSOA形成的贡献。
