Theoretical Study on Surface Structure and Mass Transfer at Atmospheric Aerosols

本研究旨在通过分子模拟和流体动力学模拟来了解非均匀大气化学，特别是气溶胶表面的结构和质量传输。一个特别的重点是放在以前的评估质量的气体物种进入液体表面的适应系数，在大气建模中的重要参数，因为它是不简单的估计这些系数单独通过实验室实验。为了帮助精确分析吸收实验，我们进行了液滴串流管实验的计算流体动力学模拟，并定量评估了在流管的现实条件下的气相中的传输。模拟结果表明，经过对气相扩散过程的仔细校正后，前人的水凝结实验与分子动力学模拟结果基本雅阁。作为该项目的最后一年，我们在《Chemistry Reviews》上发表了一份综述论文，总结了我们今年的研究成果。本项目的另一个重点是发展界面和频光谱（SFG）的理论和模拟方法，以研究与大气化学相关的液体界面。我们提出了非经验分析的SFG光谱的从头算分子模拟和分子动力学模拟的帮助下。今年，我们对水面SFG计算进行了修订，证明计算的准确性有了显着提高。在SFG计算方面，我们在密度泛函理论的基础上扩展了电荷响应核理论。发展灵活的、可极化的分子模型是SFG模拟普遍应用必不可少的步骤。我们计划将修订和改进的分子模型应用于各种界面的SFG分析。

This study aims at understanding heterogeneous atmospheric chemistry, particularly surface structure and mass transfer at aerosol surfaces, by molecular simulations and fluid dynamics simulations. A particular focus is put on the previous evaluation of mass accommodation coefficients of gas species into liquid surfaces, important parameters in atmospheric modeling, since it is not straightforward to estimate these coefficients by laboratory experiments alone. To help precisely analyze uptake experiments, we performed computational fluid dynamics simulation of the droplet train flow tube experiments, and quantitatively evaluated the transport in the gas phase at realistic conditions of the flow tube. The simulation suggested that previous experiment of water condensation is actually in accord with molecular dynamics simulation, after careful calibration of the gas-phase diffusion. As the final year of this project, we summarized our studies this year in a review paper of Chemistry Reviews.Another focus of this project is development of theory and simulation methods for interfacial sum frequency generation (SFG) spectroscopy, toward investigating liquid interfaces relevant to atmospheric chemistry. We proposed non-empirical analysis of SFG spectroscopy with the help of ab initio molecular modeling and molucular dynamics simulations. This year we performed revised SFG calculation for water surface, demonstrating significant improvement in accuracy of the calculations. In connection to the SFG calculation, we have extended the charge response kernel theory on the basis of the density functional formalism. Development of flexible and polarizable molecular modeling is a indispensable step for use of general application of SFG simulation. We plan to apply the revised and improved molecular model to SFG analysis of a wide variety of interfaces.