Time-Resolved Electrospray Mass Spectrometric Studies of Atmospheric Gas-liquid Reactions

重要但缺乏约束的多相化学途径限制了目前对大气处理和挥发性有机化合物全球预算的理解。电喷雾质谱（ES-MS）是研究液体微射流界面反应的有力工具，具有高时间分辨率。该方法允许在没有二次化学反应的情况下同时检测反应物、初级产物和中间体，用于现实条件下的各种化学反应。通过这个项目，PI将把气束调制和脉冲离子门控检测技术结合到他现有的耦合反应器和ES-MS系统中。新方法将在没有外场的情况下解决水滴表面的反应事件。该仪器将用于研究微酸性水体表面生物气体的非均相化学性质。先前的证据表明，在pH值低于4的空气-水界面上，弱水合的h30 +能够使非烷烃有机气体质子化。在典型的环境表面上，生物源烯烃很可能发生类似的质子化和阳离子低聚化。这一现象将为大多数挥发性有机气体的干沉积提供一个普遍的机制。该项目将利用基于新提出的技术的创新实验方法解决全球大气化学中的重要问题。研究结果有望填补目前对生物气体和二次气溶胶形成的大气化学理解的空白，并为大气中二氧化碳在水中的清除和随后的空气到水的转移提供基本的见解。该项目将(1)帮助解决对大气化学很重要的多相界面过程，从而为更现实的模型机制奠定基础；(2)使学生接触到全球环境化学中新的、更广泛的视角和技能。教育和拓展活动包括指导一名博士后、一名研究生和一名本科生。教育机会将扩大到社区大学学生（通过与橡树顶科学研究所的合作）和传统上代表性不足的群体成员（通过加州理工学院的MURF项目和与帕萨迪纳城市学院的合作）。

Important but poorly constrained multiphase chemical pathways limit current understanding of the atmospheric processing and global budgets of volatile organic compounds. Electrospray mass spectrometry (ES-MS) is a powerful tool with which to investigate interfacial reactions on liquid microjets at high temporal resolution. The approach allows simultaneous detection of reactants, primary products, and intermediates in the absence of secondary chemistry for a wide variety of chemical reactions under realistic conditions. Through this project, the PI will incorporate a technique of gas-beam modulation and pulsed ion-gating detection to his existing coupled reactor and ES-MS system. The new approach will resolve reactive events on surfaces of water droplets in the absence of an applied external field. The new instrument will be used to investigate the heterogeneous chemistry of biogenic gases on the surface of mildly acidic water. Previous evidence indicates that the weakly hydrated H3O+ in small water clusters is able to protonate non-alkane organic gases at the air-water interface below pH 4. It is likely that biogenic olefins would be similarly protonated and engage in cationic oligomerization on typical environmental surfaces. This phenomenon would provide a universal mechanism for the dry deposition of most volatile organic gases. The project will addresses important issues in global atmospheric chemistry using innovative experimental approaches based on a newly proposed technique. Results are expected to fill outstanding gaps in current understanding of the atmospheric chemistry of biogenic gases and secondary aerosol formation and provide fundamental insight into the scavenging and subsequent air-to-water transfer of atmospheric CO2 on water. The project will (1) help resolve multi-phasic interfacial processes that are important to atmospheric chemistry and thereby lay the foundation of more realistic model mechanisms and (2) expose students to new, wider perspectives and skills in global environmental chemistry. Education and outreach activities include mentoring a postdoctoral fellow, a graduate student, and undergraduate students. Educational opportunities will be extended to community college students (through a partnership with Oak Crest Institute of Science) and to members of traditionally underrepresented groups (through Caltech's MURF program and a collaboration with Pasadena City College).