Collaborative Research: Why Does Oxidation Improve Freezing? Using Laboratory Measurements and Molecular Simulations to Investigate Heterogeneous Ice Nucleation on Carbon Surfaces

化学学部的环境化学科学（ECS）项目支持Sarah D. Brooks（德克萨斯农工大学）和Valeria Molinero（犹他大学）的合作研究工作，利用实验室测量和分子模拟的前所未有的结合来研究模型有机表面和烟灰上冰的非均质成核。该项目的主要目标是评估碳质表面的哪些特定化学和物理性质调节了它们作为冰核冻结水的能力。第二个目标是阐明这些表面冰形成的非均匀机制。先前的实验室结果表明，代表大气老化的氧化过程提高了气溶胶的冰核能力，促进了在较高温度下的接触冻结。然而，氧化不仅通过掺入亲水性基团，而且通过修饰表面的纳米结构来改变碳表面。将进行实验室实验，以确定碳氢化合物和氧化碳氢化合物颗粒浸泡和沉积冻结所需的先决温度和相对湿度。模拟将用于确定纳米结构、化学修饰和表面亲水性对冻结温度的影响，冰形成的非均质机制，以及临界冰胚的大小和结构。由于人为和生物源的原因，碳质颗粒在大气中含量丰富，在促进云中冰的成核方面表现出广泛的有效性。这种可变性导致气溶胶对气候影响的预测存在很大的不确定性。该项目将使人们更好地了解大气中水的状态，并有助于全球气候模式的参数化。犹他大学将举办一个讲习班，培训高中教师如何使用免费提供的分子可视化软件，以开展补充和加强高中课程的课堂活动。分子可视化工具和模拟显示冰的形成将被纳入pi教授的本科课程。

The Environmental Chemical Sciences (ECS) program of the Division of Chemistry supports the collaborative research efforts of Sarah D. Brooks (Texas A&M University) and Valeria Molinero (University of Utah) to investigate the heterogeneous nucleation of ice on model organic surfaces and soot using an unprecedented combination of laboratory measurements and molecular simulations. The primary objective of this project is to evaluate which specific chemical and physical properties of carbonaceous surfaces modulate their ability to act as ice nuclei for water freezing. The second objective is to elucidate the heterogeneous mechanisms of formation of ice on these surfaces. Previous laboratory results suggest that oxidation processes representative of atmospheric aging improve the ice nucleating ability of aerosols, facilitating contact freezing at warmer temperatures. Oxidation, however, alters carbon surfaces not only by incorporation of hydrophilic groups but also through a modification of the nanostructure of the surface. Laboratory experiments will be conducted to determine the prerequisite temperature and relative humidity required for immersion and deposition freezing on hydrocarbon and oxidized hydrocarbon particles. Simulations will be used to determine the effect of nanostructure, chemical modifications, and hydrophilicity of the surface on the freezing temperatures, the heterogeneous mechanism of formation of ice, and the size and structure of the critical ice embryo. Abundant in the atmosphere due to anthropogenic and biogenic sources, carbonaceous particles display a wide range of effectiveness in promoting the nucleation of ice in clouds. This variability causes major uncertainties in predictions of the effect of aerosols on climate. The project will lead to an improved understanding of the phase of water in the atmosphere and assist in the parameterization of global climate models. A workshop to train high school teachers in the use of freely available molecular visualization software to develop classroom activities that complement and enhance the high-school curriculum will be developed at the University of Utah. The molecular visualization tools and the simulations that display the formation of ice will be incorporated into undergraduate courses taught by the PIs.