Aerosol Growth and Chemical Compositions from Heterogeneous Processing of Organic Compounds

本项目要解决的科学问题包括：(1)不同类别的含氧有机化合物对无机、有机和烟尘气溶胶进行多相处理的化学机制是什么；(2)多相处理对气态反应物浓度、相对湿度、反应时间以及颗粒的酸度和大小有何依赖；(3)第一代和后续几代低和半挥发性有机化合物(VOC)氧化产物之间的协同效应以及颗粒相中氧化剂的存在的影响；以及(4)如何利用实验室测量来辅助解释大气有机颗粒物(PM)的环境测量和模拟？通过将流动反应器中的单分散气溶胶和沉积在光学元件中的颗粒暴露于低浓度的VOC氧化代表性产物(包括α-二羰基、醛和醇)的气体浓度，将研究非均相处理。实验还将在特氟龙室中进行，气雾剂暴露在VOCs光氧化现场产生的有机化合物中。二次有机气溶胶(SOA)的增长将通过同时测量颗粒大小、质量、密度和化学成分以及气态有机浓度来量化。在不同相对湿度(RH)、酸度和反应时间的条件下，将选择种子粒子来代表初级和次级大气气溶胶。使用串联式差分迁移率分析仪(TDMA)和差动迁移率分析仪-气溶胶粒子质量分析仪(DMA-APM)相结合的方法测量由于异质加工引起的颗粒大小和质量的变化。气态反应物的浓度将通过离子漂移-化学电离串联质谱仪(ID-CIMS/MS)进行监测。利用热解吸-离子漂移-化学电离串联质谱仪(TD-ID-CIMS/MS)、衰减全反射傅里叶变换红外光谱(ATR-FTIR)、核磁共振(NMR)光谱和基质辅助激光解吸/电离飞行时间质谱仪(MALDI-TOFMS)表征气溶胶粒子的化学组成。持续暴露在高水平的颗粒物中会对人类健康产生不利影响。此外，气溶胶在调节地球-大气系统的太阳辐射吸收方面也起着重要的作用。了解有机气溶胶的形成和生长是大气化学和气溶胶研究的前沿。该项目产生的有机气溶胶的形成和化学成分的信息可用于评估对人类健康的影响，包括呼吸系统和心血管疾病。因此，这项研究不仅将增进我们对有机气溶胶形成的认识，而且将有助于公众识别潜在的人类健康和气候问题，并有助于政策制定者制定有效的环境颗粒物控制策略。该项目将为有机化学和大气科学领域的本科生和研究生提供跨学科的研究机会。他们将有机会在会议上介绍他们的工作，并在两个科学界建立联系，作为其关于全球环境变化研究的教育和培训的一部分。

Scientific questions to be addressed in this project include (1) what is the chemical mechanism of heterogeneous processing of different classes of oxygenated organic compounds on inorganic, organic, and soot aerosols, (2) what is the dependence of heterogeneous processing on gaseous reactant concentrations, RH, reaction time, and particle acidity and size, (3) what are synergetic effects between the first- and later generations of low and semi-volatile organic compounds (VOC) oxidation products and effects of the presence of oxidants in the particle phase, and (4) how can laboratory measurements be used to aid interpretation of ambient measurements and simulations of atmospheric organic particulate matter (PM)? Heterogeneous processing will be studied by exposing monodisperse aerosols in a flow reactor and particles deposited in an optical cell to low gaseous concentrations of representative products from VOC oxidation, including alpha-dicarbonyls, aldehydes, and alcohols. Experiments will also be conducted in a Teflon chamber with aerosols exposed to organic compounds generated in situ from photo-oxidation of VOCs. Secondary organic aerosol (SOA) growth will be quantified from concurrent measurements of the particle size, mass, density, and chemical compositions along with the gaseous organic concentrations. Seed particles will be chosen to represent primary and secondary atmospheric aerosols under conditions of different relativity humidity (RH), acidity, and reaction times. The changes in the particle size and mass due to heterogeneous processing will be measured using a combination of tandem differential mobility analyzer (TDMA) and differential mobility analyzer - aerosol particle mass analyzer (DMA-APM). Concentrations of gaseous reactants will be monitored by ion drift - chemical ionization tandem mass spectrometry (ID-CIMS/MS). The chemical composition of aerosol particles will be characterized using thermal desorption - ion drift - chemical ionization tandem mass spectrometry (TD-ID-CIMS/MS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), nuclear magnetic resonance (NMR) spectrometry, and matrix-assisted laser desorption/ionization - time-of-flight mass spectrometry (MALDI-TOFMS). Persistent exposure to elevated levels of particulate matter has adverse effects on human health. Also, aerosols play an important role in regulating the solar radiation intake in the earth-atmosphere system. Understanding of formation and growth of organic aerosols represents a frontier in atmospheric chemistry and aerosol research. The information on formation and chemical compositions of organic aerosols generated from this project can be employed to assess human-health effects including respiratory and cardiovascular diseases. Hence, this research not only will advance our knowledge of organic aerosol formation, but also will be beneficial to the public by identification of potential human health and climate issues and to policy-decision makers in developing effective control strategies for ambient particulate matter. The project will provide interdisciplinary research opportunities for undergraduate students and graduate students in the areas of organic chemistry and atmospheric sciences. They will have the opportunity to present their work at conferences and build connections within the two scientific communities, as part of their education and training on global environmental change research.