Formation of Secondary Organic Aerosol by Aqueous-phase Reactions of Phenols

大气颗粒具有广泛的影响，从损害人类健康到改变地球气候。然而，关于这些颗粒的来源，特别是大气中形成的含碳颗粒，即二次有机气溶胶（SOA）的来源，人们仍然知之甚少。直到最近，人们还认为SOA只能由大气中有机气体的反应形成，但最近的研究表明，SOA也可以由云雾滴和含有少量水的气溶胶颗粒的反应形成。可能通过水相反应对SOA做出重大贡献的一类化合物是酚类。木材和其他生物质的燃烧通过住宅木材燃烧和野火等来源排放出大量酚类物质。这些化合物是相当水溶性的，在溶液中反应迅速，有效地形成大的，低挥发性的产品。鉴于这些性质，酚类物质很可能是水相SOA的重要来源。现有的关于大气中酚类物质的少量研究与这一观点一致，但对作为二次有机气溶胶来源的酚类物质的水相反应还没有深入的研究。该研究将彻底表征水苯酚反应作为SOA的来源，并将估计这一途径对大气颗粒负担的贡献。这将通过四个目标来实现：1)测量在各种条件下由水相苯酚形成SOA的速率，以模拟云/雾滴和水相气溶胶颗粒；2)量化苯酚水相反应中SOA的产率；3)使用三种互补的技术对SOA进行化学表征；4)使用速率、产率和表征数据来估计水相中苯酚氧化作为SOA来源的重要性。大多数研究将使用定义明确的单个和混合酚的实验室溶液进行，在实验室中使用在大气水滴和含水颗粒中重要的特定反应途径进行研究。还将研究从木材燃烧释放的复杂气体混合物的水反应中形成SOA。SOA产量将通过重量质量、高分辨率气溶胶质谱（HR-AMS）和傅里叶变换红外光谱（FTIR）来确定。后两种技术与液相色谱和高分辨率质谱相结合，也将用于表征SOA的元素、官能团和分子特征。本研究将指导三名研究生。主要研究人员还将把该研究项目的一些方法和结果整合到他们的本科和研究生教学中，包括一门关于先进大气仪器的新研究生课程。该项目还将包括与加州大学戴维斯分校空气质量研究中心合作的外展部分：学生（主要是中学生）将来到校园参加为期一天或两天的课程，接受有关大气颗粒和空气污染的实践课程。

Atmospheric particles have a wide range of impacts, from damaging human health to altering the earth's climate. And yet a great deal is still not known about the sources of these particles, especially for carbon-containing particles formed in the atmosphere, i.e., secondary organic aerosols (SOA). Until recently it was thought that SOA was only formed from reactions of organic gases in the atmosphere, but more recent work has shown that SOA can also be formed from reactions in cloud and fog drops and aerosol particles containing small amounts of water. One group of compounds that is likely to make a significant contribution to SOA via aqueous phase reactions are the phenols. Large amounts of phenols are emitted from the combustion of wood and other biomass through sources such as residential wood combustion and wild fires. These compounds are quite water soluble and react rapidly in solution to efficiently form large, low volatility products. Given these properties, it is likely that phenols are a significant source of aqueous-phase SOA. The few available studies of atmospheric phenols are consistent with this idea, but there has been no thorough study of the aqueous-phase reactions of phenols as a source of secondary organic aerosol. The research will thoroughly characterize aqueous phenol reactions as a source of SOA and will estimate the contribution of this pathway to the atmospheric burden of particles. This will be accomplished through four objectives: 1) Measure the rates of SOA formation from aqueous phenols under a variety of conditions to mimic both cloud/fog drops and aqueous aerosol particles; 2) Quantify the yields of SOA from aqueous-phase reactions of phenols; 3) Chemically characterize the SOA using three complementary techniques; and 4) Use the rate, yield, and characterization data to estimate the significance of phenol oxidation in aqueous phases as a source of SOA. Most of the research will be performed using well-defined laboratory solutions of individual and mixed phenols studied in the laboratory using specific reaction pathways that are important in atmospheric water drops and water-containing particles. The formation of SOA from aqueous reactions of the complex mixture of gases emitted from the combustion of wood will also be studied. SOA yields will be determined using gravimetric mass, high-resolution Aerosol Mass Spectrometry (HR-AMS), and Fourier Transform Infrared spectrometry (FTIR). These latter two techniques, in conjunction with liquid chromatography coupled to high-resolution mass spectrometry, will also be used to characterize the elemental, functional group, and molecular characteristics of the SOA.Three graduate students will be mentored through the research. The principal investigators will also integrate some of the approaches and results from this research project into their undergraduate and graduate teaching, including a new graduate course on advanced atmospheric instrumentation. The project will also include an outreach component in conjunction with the University of California - Davis Air Quality Research Center: students (primarily in middle school) will come to campus for a one- or two-day program to receive hands-on lessons about atmospheric particles and air pollution.