Surfaces of Secondary Organic Aerosol Particles

在这个由化学学部环境化学科学项目资助的项目中，西北大学的弗朗茨·盖格和里根·汤姆森教授以及哈佛大学的斯科特·马丁教授正在开发新的方法来研究由世界热带和北方森林上空的植物排放形成的大气气溶胶颗粒的表面。气溶胶颗粒的表面是分子在导致颗粒生长和随后形成云的过程中从气相接近颗粒时首先遇到的物质。粒子表面是一个具有挑战性的区域，因为它很薄，非常活跃。该团队专门探测气溶胶颗粒表面、颗粒体积和气相，然后专注于识别居住在大气气溶胶气相和颗粒相之间的化合物。研究小组还确定了这些表面化合物是如何促进或破坏颗粒生长的，以及它们形成云的倾向。合成的化合物可供研究界使用，从而实现跨越传统学科界限的新合作。大气化学领域需要受过交叉学科训练的工作人员。项目提供的协作性培训解决了跨学科研究活动的需求。拟议的活动还结合了对多样性的有意义的关注。对研究生进行严格的培训和指导，包括在西北大学和哈佛大学进行研究轮转，在拨款申请写作方面进行正式培训，在合成化学和光谱学方面进行跨学科培训，气溶胶样本收集和分析，以及参与社区外展项目。建议的活动通过定期评估和评价进行微调。本研究项目验证了二级有机气溶胶（SOA）粒子的生长及其作为云凝结核（CCN）的倾向可能受到表面化学的显著影响的假设。通过合成氘化和未标记的异戊二烯和á-pinene及其纯形式的氧化产物，从这些前体制备SOA颗粒，以及(3)通过测量获得表面和体积特异性光谱，化学和机制信息，以确定表面定位的物种如何促进SOA生长和CCN活性。该研究包括新的合成和测量方法，揭示了在不同相对湿度和粒径条件下颗粒表面化学对颗粒生长的影响的独特物理见解。以下五个首要的科学问题被解决：哪些有机物种划分到SOA粒子的表面？表面定域物质的停留时间是多少？界面物质扩散到体粒子相的程度是多少？气相物质对SOA粒子表面的吸附是可逆的还是不可逆的？哪些表面物质通过作为表面活性剂池来增加CCN活性？是否有一些表面物种对粒子的进一步生长形成屏障（吸引子），从而抑制（刺激）粒子的进一步生长？

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?