Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey 08544, United States.
High Meadows Environmental Institute, Princeton University, Princeton, New Jersey 08544, United States.
Environ Sci Technol. 2023 Sep 5;57(35):13092-13103. doi: 10.1021/acs.est.2c09627. Epub 2023 Aug 22.
Interactions between water and organic molecules in sub-4 nm clusters play a significant role in the formation and growth of secondary organic aerosol (SOA) particles. However, a complete understanding of the relevant water microphysics has not yet been achieved due to challenges in the experimental characterization of soft nuclei. Here, we use molecular dynamics simulations to study the phase-mixing states, surface tension, water activity, and water accommodation coefficient of organic-water clusters representative of freshly nucleated SOA particles. Our results reveal large deviations from the behavior expected based on continuum theories. In particular, the phase-mixing state has a strong dependence on cluster size; surface tension displays a minimum at a specific organic-water mass ratio (/ ∼ 4.5 in this study) corresponding to a minimum inhibition of droplet nucleation associated with the Kelvin effect; and the water accommodation coefficient increases by a factor of 2 with nanocluster hygroscopic growth, in agreement with recent experimental studies. Overall, our results yield parametric relations for water microphysical properties in sub-4 nm clusters and provide insight into the role of water in the initial stages of SOA nucleation and growth.
在亚 4nm 团簇中，水和有机分子之间的相互作用在二次有机气溶胶 (SOA) 颗粒的形成和生长中起着重要作用。然而，由于软核的实验特性描述存在挑战，相关水微观物理学仍未被完全理解。在这里，我们使用分子动力学模拟来研究具有代表性的新鲜成核 SOA 颗粒的有机-水团簇的相混合状态、表面张力、水活度和水容纳系数。我们的结果显示出与连续体理论预期的行为有很大的偏差。特别是，相混合状态强烈依赖于团簇尺寸；表面张力在特定的有机-水质量比 (/ ∼ 4.5 在本研究中) 处显示最小值，这对应于与 Kelvin 效应相关的液滴成核抑制的最小值；水容纳系数随着纳米团簇吸湿性生长增加了 2 倍，这与最近的实验研究一致。总的来说，我们的结果提供了亚 4nm 团簇中水分微观物理性质的参数关系，并深入了解了水在 SOA 成核和生长初始阶段的作用。
