Collaborative Research: Impact of Surface Chemistry for Black Carbon Cloud Droplet Formation

该奖项由化学学部环境化学科学项目资助。约翰霍普金斯大学的Howard Fairbrother教授和马里兰大学帕克分校的Akua a . Asa-Awuku教授得到了支持，他们将从分子水平上理解烟灰（黑碳，BC）表面的化学成分如何影响其作为云凝结核（CCN）和形成雨滴的能力。森林火灾、生物质燃烧、煤炭和柴油发动机释放出黑碳颗粒到地球大气中。实验证据有力地支持了黑碳颗粒吸水能力取决于黑碳颗粒表面是否存在吸水官能团的观点。然而，在科学模型中，大气中的黑碳被认为是防水的，因此在气溶胶-云气候相互作用中没有得到适当的解决，这是气候预测中最大的不确定性来源。由于碳源、燃烧条件和随后在空气中氧化（老化）的不同，黑碳颗粒的表面化学性质很复杂，变化很大。该项目旨在更好地了解表面反应性如何影响黑碳作为云凝结核的能力。建立大气中BC颗粒的表面化学和CCN特性之间的关系，提高了全球气候模式的预测能力，增强了我们对空气质量和气候这两个重要社会问题的科学认识。在进行项目的过程中，学生受益于获得表面化学和大气科学的技能。马里兰圣母大学（Notre Dame University of Maryland）是一所以教学为主的地方大学，一项针对理科专业女本科生参与的计划启动了。该项目旨在从分子水平上了解黑碳表面的化学成分如何影响其作为云凝结核（CCN）的能力。目标是通过测量和分析一系列黑碳颗粒的CCN特性来实现的，这些黑碳颗粒的表面化学成分通过暴露于不同的氧化条件而系统地发生变化。具体任务是开发实验方法来修饰和表征与大气相关的气溶胶的化学和表面性质，并解决BC对大气CCN的未知贡献以及随后的气溶胶间接效应。通过各种分析技术，包括x射线光电子能谱，化学衍生化和红外光谱，可以获得表面氧化物的表面组成和分布的详细信息。研究人员还探讨了其他杂原子对CCN性质的影响，以及CCN活化与更基本的BC表面性质（如水吸附能）之间的关系。

This award is funded by the Environmental Chemical Sciences Program in the Division of Chemistry. Professors Howard Fairbrother of Johns Hopkins University and Akua A. Asa-Awuku of the University of Maryland College Park are supported to develop a molecular level understanding of how the chemical composition of the surface of soot (black carbon, BC) influences its ability to act as Cloud Condensation Nuclei (CCN) and form rain droplets. Black carbon particles are released into the Earth's atmosphere from forest fires, biomass burning, and coal and diesel engines. Experimental evidence provides strong support for the idea that the ability of black carbon particles to uptake water depends on the presence of water-attracting functional groups on the black carbon particle surface. However, atmospheric black carbon is considered water-repellant in scientific models and thus not aptly addressed in aerosol-cloud climate interactions, contributing to the largest source of uncertainty in climate predictions. The surface chemistry of black carbon particles is complex and varies considerably due to differences in the carbon source, combustion conditions and subsequent oxidation (aging) in air. This project seeks a better understanding of how surface reactivity influences black carbon's ability to act as cloud condensation nuclei. Establishing relationships between the surface chemistry and CCN properties of BC particles in the atmosphere improves the predictive capabilities of global climate models and enhances our scientific understanding of air quality and climate, two important societal concerns. While conducting the project, the students benefit from acquiring skills in surface chemistry and atmospheric science. A plan that targets the participation of female undergraduate students in science majors at the Notre Dame University of Maryland, a local, primarily teaching, institution is initiated. The project aims to develop a molecular level understanding of how the chemical composition of the surface of black carbon influences its ability to act as Cloud Condensation Nuclei (CCN). The goal is accomplished by measuring and analyzing the CCN properties of a suite of black carbon particles whose surface chemistry has been systematically varied via exposure to different oxidizing conditions. The specific tasks are to develop experimental methods to modify and characterize the chemistry and surface properties of atmospherically-relevant aerosol, and to address unknown contributions of BC to atmospheric CCN and the subsequent aerosol-indirect effect. Detailed information on the surface composition and distribution of surface oxides is obtained with various analytical techniques, including X-ray Photoelectron Spectroscopy, augmented by chemical derivatization and infrared spectroscopies. The effect of other heteroatoms on CCN properties is also explored as well as the relationship between CCN activation and more fundamental BC surface properties, such as water adsorption energies.