Surfaces of Secondary Organic Aerosol Particles

在这个由化学系环境化学科学计划资助的项目中，西北大学的Franz Geiger教授和Regan Thomson教授以及哈佛大学的Scot Martin教授正在开发新的方法来研究世界热带和北方森林上空由植物排放形成的大气气溶胶颗粒的表面。气溶胶粒子的表面是分子从气相接近粒子时遇到的第一个物种，在导致粒子生长和随后的云形成的过程中。颗粒表面是一个具有挑战性的物质区域，因为它很薄，而且非常活泼。该团队专门探测气溶胶颗粒表面、颗粒体和气相，然后专注于识别存在于大气气溶胶的气相和颗粒相之间的边界上的化合物。该团队还确定了这些表面化合物如何促进或破坏粒子生长及其形成云的倾向。合成的化合物可供研究界使用，使跨越传统学科界限的新合作成为可能。大气化学领域需要一支受过交叉学科培训的工作队伍。该项目提供的协作培训通过跨学科研究活动满足需要。拟议的活动还结合了对多样性的有意义的关注。为研究生提供严格的培训和指导经验，包括在西北大学和哈佛大学的研究轮换，撰写拨款申请的正式培训，合成化学和光谱学的跨学科培训，气溶胶样本收集和分析，以及参与社区外联计划。这项研究项目测试了二次有机气溶胶(SOA)粒子的增长及其作为云凝结核(CCN)的倾向会受到表面化学的显著影响的假设。通过合成纯形式的氢化和未标记的异戊二烯和α-蒎烯及其氧化产物，从这些前体制备SOA颗粒，以及(3)通过测量获得表面和本体特定的光谱、化学和机理信息，以确定表面定域物种如何对SOA生长和CCN活性做出贡献，来检验这些假设。这项研究包括新的合成和测量方法，揭示了在不同的相对湿度和颗粒大小条件下，颗粒表面化学如何对颗粒生长起重要作用的独特物理见解。以下五个最重要的科学问题被解决了：哪些有机物种被分配到SOA颗粒的表面？表面定域物种的停留时间是多少，界面物种扩散到块体颗粒相的程度如何？气相物质是可逆还是不可逆地吸附在SOA颗粒表面？哪些表面物种通过充当表面活性剂池来增加CCN的活性？某些表面物种是否存在阻碍颗粒进一步生长的障碍(吸引子)，从而抑制(刺激)颗粒的进一步生长？

In this project, funded by the Environmental Chemical Science Program of the Chemistry Division, Professors Franz Geiger and Regan Thomson of Northwestern University and Professor Scot Martin of Harvard University are developing new methods to investigate the surfaces of atmospheric aerosol particles formed from plant emissions over the world's tropical and boreal forests. The surface of aerosol particles is the first species encountered by molecules approaching the particles from the gas phase in processes leading to particle growth and subsequent cloud formation. The particle surface is a challenging region of matter to access experimentally because it is thin and very reactive. The team specifically probe aerosol particle surfaces, the particle bulk, and the gas phase and then focuses on identifying chemical compounds residing at the boundary between the gas and particle phases of atmospheric aerosols. The team also determines how these surface compounds promote or disrupt particle growth and their propensity to form clouds. The synthesized compounds are available to the research community, enabling new collaborations that cross traditional disciplinary boundaries. The field of atmospheric chemistry requires a workforce trained in crosscutting disciplines. The collaborative training provided by the project addresses that need through interdisciplinary research activities. The proposed activities are also integrated with a meaningful focus on diversity. Rigorous training and mentoring experiences for graduate students includes research rotations at Northwestern and Harvard Universities, formal training in grant proposal writing, cross-disciplinary training in synthetic chemistry and spectroscopy, aerosol sample collection and analysis, and participation in community outreach programs. The proposed activities are fine-tuned by regular assessment and evaluation.This research project tests the hypotheses that the growth of secondary organic aerosol (SOA) particles and their propensity to act as cloud condensation nuclei (CCN) can be significantly influenced by surface chemistry. The hypotheses is tested by synthesizing both deuterated and unlabeled isoprene and á-pinene and their oxidation products in pure forms, preparing SOA particles from these precursors, and (3) obtaining through measurement surface- and bulk-specific spectroscopic, chemical, and mechanistic information for determining how the surface-localized species contribute to SOA growth and CCN activity. The research includes new synthesis and measurement approaches that reveal unique physical insights of how particle surface chemistry matters for particle growth under varying conditions of relative humidity and particle size. The following overarching five science questions are addressed: Which organic species partition to the surface of SOA particles? What are the residence times of the surface-localized species, and to what extent does diffusion of the interfacial species occur into the bulk particle phase? Do gas phase species adsorb reversibly or irreversibly to the surfaces of SOA particles? Which surface species increase CCN activity by acting as a surfactant pool? Do some surface species present a barrier (attractor) to further particle growth and thereby inhibit (spur) further particle growth?