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大气的非均质化学，特别是气溶胶表面的表面结构和传质。特别的重点放在先前对气体进入液体表面的质量调节系数的评估上，这是大气模拟中的重要参数，因为仅通过实验室实验估计这些系数并不直接。为了精确分析吸收实验，我们对液滴列流管实验进行了计算流体动力学模拟，定量评估了实际条件下液滴列流管在气相中的输运。经过对气相扩散的仔细校正，模拟结果表明，先前的水凝聚实验实际上与分子动力学模拟是一致的。作为这个项目的最后一年，我们在Chemistry Reviews的一篇综述文章中总结了这一年的研究。该项目的另一个重点是开发界面和频率产生（SFG）光谱的理论和模拟方法，以研究与大气化学相关的液体界面。我们提出了利用从头算分子模型和分子动力学模拟对SFG光谱进行非经验分析的方法。今年我们对水面进行了修正后的SFG计算，计算精度有了明显提高。结合SFG的计算，我们在密度泛函形式的基础上扩展了电荷响应核理论。柔性和可极化分子模型的开发是实现SFG模拟的普遍应用必不可少的一步。我们计划将修正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.