Theoretical Study on Surface Structure and Mass Transfer at Atmospheric Aerosols

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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.