Heterogeneous Chemistry of Gas-Phase Intermediates in the OH-oxidation of Dimethyl Sulfide

在化学系环境化学科学项目的支持下，麦迪逊威斯康星大学的蒂莫西·伯特伦教授和他的学生正在研究与大气相关的硫磺化学。从表层海洋排放的挥发性有机化合物在地球大气中被氧化，形成低挥发性分子，这些分子可以形成新的气溶胶颗粒或凝结到现有的气溶胶颗粒上。二甲基硫化物(DMS)是海洋大气中还原硫的最丰富来源，在海洋环境中气溶胶粒子的形成和生长中起着核心作用。尽管二甲基硫在地球气候中很重要，但对二甲基硫氧化的中间产物的全面了解有限，导致对硫酸和甲磺酸(MSA)产量的估计存在很大差异，这两个产量是二甲基硫氧化的关键终点。本项目将研究DMS氧化过程中关键中间体的非均相动力学，以及它们如何调节硫酸和MSA的生产。该项目将支持一个化学研究生的博士论文和多个本科生的论文项目。研究团队将继续参与密歇根大学麦迪逊分校的化学招生计划(CHOPS，化学机会)和通往化学博士学位的桥梁计划，该计划旨在支持化学领域代表性不足的学生。此外，研究小组将与当地的K-12学校合作，测量和评估公立学校的室内空气质量。该项目将使用实验室测量来：1)量化DMS的羟基氧化反应中关键中间体的异相和多相反应的速率，以及2)确定气溶胶和云水中氢过甲硫甲酸甲酯(HPMTF)的缩合相反应的产物产量和化学机理。具体地说，使用与化学电离质谱仪耦合的携带气溶胶流动反应器，该团队将确定二甲基亚砜(DMSO)、甲磺酸(MSIA)、MSA和HPMTF对具有代表性的海洋气溶胶模拟物(例如海雾、硫酸铵)的反应吸收系数，作为相对湿度和颗粒酸度的函数。利用在线和离线采样技术的组合，将确定HPMTF在云水和海洋气溶胶模拟物中的凝聚相反应的产物产率。预计这将允许更准确地评估形成硫酸盐气溶胶的DMS排放的比例。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Environmental Chemical Sciences Program of the Division of Chemistry, Professor Timothy Bertram and his students at the University of Wisconsin, Madison are studying sulfur chemistry related to the atmosphere. Volatile organic compounds, emitted from the surface ocean, are oxidized in the earth atmosphere resulting in the formation of low volatility molecules that can nucleate new aerosol particles or condense onto existing aerosol particles. Dimethyl sulfide (DMS) is the most abundant source of reduced sulfur to the marine atmosphere and plays a central role in the formation and growth of aerosol particles in marine environments. Despite the importance of DMS in climate on earth, a comprehensive understanding of the intermediate products in the oxidation of DMS is limited, leading to large variability in estimates of sulfuric acid and methanesulfonic acid (MSA) yields; the key endpoints of DMS oxidation. This project will investigate the heterogeneous kinetics of key intermediates in the oxidation of DMS and how they regulate the production of sulfuric acid and MSA. This project will support the PhD thesis for one chemistry graduate student and multiple undergraduate thesis projects. The research team will continue to be involved the UW Madison chemistry recruitment program (CHOPS, CHemistry OPportunitieS) and the Bridge to the Chemistry Doctorate program designed to support underrepresented students in chemistry. Additionally, the research team will partner with local K-12 schools on the measurement and assessment of indoor air quality in public schools.This project will use laboratory measurements to: 1) quantify the rate of heterogeneous and multiphase reactions of key intermediates in the OH-oxidation of DMS and 2) determine the product yields and chemical mechanism for the condensed phase reaction of hydroperoxymethyl thioformate (HPMTF) in aerosol and cloud water. Specifically, using an entrained aerosol flow reactor coupled to a chemical ionization mass spectrometer, the team will determine the reactive uptake coefficient of dimethyl sulfoxide (DMSO), methanesulfinic acid (MSIA), MSA and HPMTF to representative marine aerosol mimics (e.g., sea spray, ammonium sulfate) as a function of relative humidity and particle acidity. Using a combination of online and offline sampling techniques, the product yields for the condensed phase reactions of HPMTF in cloud water and marine aerosol mimics will be determined. This is expected to permit a more accurate assessment of the fraction of DMS emitted that forms sulfate aerosol.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.