Department of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology , S-10691 Stockholm, Sweden.
J Phys Chem A. 2013 Oct 17;117(41):10746-52. doi: 10.1021/jp407538x. Epub 2013 Oct 4.
The present study illustrates the combined effect of organic and inorganic compounds on cloud droplet nucleation and activation processes representative for the marine environment. Amino acids and sea salt are common marine cloud condensation nuclei (CCN) which act as a prerequisite for growth of cloud droplets. The chemical and physical properties of these CCN play a key role for interfacial properties such as surface tension, which is important for the optical properties of clouds and for heterogeneous reactions. However, there is a lack of detailed information and in situ measurements of surface tension of such nanosized droplets. Here we present a study of the combined effect of zwitterionic glycine (ZGLY) and sea salt in nanosized water droplets using molecular dynamics simulations, where particular emphasis is placed on the surface tension for the nanosized droplets. The critical supersaturation is estimated by the Köhler equation. It is found that dissolved sea salt interacts with ZGLY through a water bridge and weakens the hydrogen bonds among ZGLYs, which has a significant effect on both surface tension and water vapor supersaturation. Clusters of glycine mixed with sea salt deliquesce more efficiently and have higher growth factors.
本研究展示了有机和无机化合物对云滴成核和激活过程的综合影响，这些过程代表了海洋环境。氨基酸和海盐是常见的海洋云凝结核（CCN），它们是云滴生长的前提。这些 CCN 的化学和物理性质对界面性质（如表面张力）起着关键作用，表面张力对云的光学性质和非均相反应都很重要。然而，对于这种纳米大小液滴的表面张力，我们缺乏详细的信息和现场测量。在这里，我们使用分子动力学模拟研究了两性离子甘氨酸（ZGLY）和海盐在纳米级水液滴中的综合影响，特别强调了纳米级液滴的表面张力。通过 Köhler 方程估计了临界过饱和度。结果表明，溶解的海盐通过水桥与 ZGLY 相互作用，并削弱 ZGLY 之间的氢键，这对表面张力和水蒸气过饱和度都有显著影响。混合有海盐的甘氨酸簇更容易潮解，生长因子更高。
