CAS: Autoxidation of Oxygenated Volatile Chemical Products in the Atmosphere

在化学系环境化学科学项目的支持下，加州理工学院的Paul Wennberg博士、Brian Stoltz博士和John Crounse博士将研究挥发性化学产品(VCP)的大气反应。VCP是含氧碳氢化合物(如乙二醇醚和酯)，是一系列产品中使用的常见溶剂，包括涂料、清洗剂和液体肥皂、除草剂、水力压裂液和织物染料。当它们被使用时，大量的这些化合物会蒸发，成为光化学的主要贡献者，产生臭氧和小颗粒(气溶胶)，导致许多城市的空气质量变差。由于车辆排放的减少，VCP的重要性也在不断增加。准确了解产生了多少臭氧和气溶胶对于了解空气质量很重要。臭氧对包括人类在内的动植物都有广泛的毒性，因为它会引起肺部和支气管炎。气雾剂使空气变得模糊，降低能见度，并与呼吸道和其他疾病有关。通过与哥本哈根大学和美国环境保护局(EPA)的合作，将对VCP的氧化化学进行模拟研究，以了解它们如何促进臭氧和空气中颗粒物的形成。除了培训学生外，该小组还将在校园和当地学校开展外展活动，解决社区高度关注的空气质量问题。了解VCP对空气质量的影响的一个主要不确定性是，它们的氧化是否会形成低挥发性化合物。特别是，自由基自氧化在它们的降解过程中可能是活跃的。通过有机过氧基的H-移位反应进行自氧化，可以从更易挥发的前体快速生成高含氧有机化合物。这些高含氧量的化合物具有低得多的蒸汽压，并凝结形成气溶胶。这项实验室和计算研究将检验这样一种假设，即许多含氧VCP中常见的乙醚部分提高了这些H-位移的速率，使自氧化成为准确描述它们在大气中降解的关键部分，从而它们对空气污染的影响。在这个项目中，研究人员将研究一组不同有机底物的这些氧化反应的速率，其中包括那些主导向大气排放含氧VCP的底物。这项工作对于理解大气中氧化有机物的成因具有潜在的重要的长期科学意义，同时也为广泛的相关挥发性有机化合物绘制了机理和产品分布。这一奖项反映了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 in the Division of Chemistry, Drs. Paul Wennberg, Brian Stoltz, and John Crounse at the California Institute of Technology will study atmospheric reactions of volatile chemical products (VCPs). VCPs are oxygen-containing hydrocarbons (such as glycol ethers and esters) that are common solvents used in a array of products, including paints, cleaning agents and liquid soaps, herbicides, hydraulic fracturing fluids, and dyes for fabrics. When they are used, large quantities of these compounds vaporize and become a major, if not the dominant, contributor to the photochemistry producing ozone and small particles (aerosols) that contribute to poor air quality in many cities. The importance of VCPs is also growing because of decreasing vehicle emissions. Accurate knowledge of how much ozone and aerosols are produced is important to understand air quality. Ozone is broadly toxic to plants and animals, including humans because it causes inflammation of the lungs and bronchia. Aerosols make the air hazy, reduce visibility and are associated with respiratory and other illnesses. Through a collaboration with the University of Copenhagen and the U.S. Environmental Protection Agency (EPA), modeling studies will be carried on the oxidative chemistry of VCPs to learn how they contribute to the formation of ozone and particles in air. In addition to training of students, the team will engage in outreach both at their campus and at local schools, addressing air quality as a topic of high interest to the community. A major uncertainty in understanding the impacts of VCPs on air quality is whether their oxidation results in formation of low volatility compounds. In particular, radical autoxidation may be active in their degradation. Autoxidation via H-shift reactions of organic peroxy radicals can rapidly produce highly oxygenated organic compounds from much more volatile precursors. These highly oxygenated compounds have a much lower vapor pressure and condense to form aerosol. This laboratory and computational investigation will examine the hypothesis that the ether moiety, common in many oxygenated VCPs, enhances the rate of these H-shifts making autoxidation an essential part of accurately describing their atmospheric degradation and thus their impact on air pollution. In this project, the investigators will study the rates of these oxidative reactions for a diverse set of organic substrates that include those that dominate the emissions of oxygenated VCPs to the atmosphere. There are potentially important long range scientific implications of this work for the understanding of the genesis of oxidized organics in the atmosphere, while at the same time mapping out mechanism and product distribution for a wide spectrum of relevant volatile organic compounds.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.