Free Energy Prediction of Ion-Induced Nucleation of Aqueous Aerosols

Abstract

Ion-induced nucleation (IIN) is thought to be an important nucleation pathway of atmospheric aerosols. We present a combined polarizable molecular dynamics (MD) simulation and the classic ion-induced nucleation theory (IINT) approach to predict the free energy profiles of the ion-induced nucleation of aqueous aerosols in a qualitative or semiquantitative way. The dependence of both cluster structure and thermodynamic properties on cluster sizes and ion species is also systemically studied. It is confirmed the ions can significantly enhance the cluster stability, and thereby increase the nucleation rate. The ability of the common atmospheric ions to enhance the nucleation rate follows the order SO 4 2− > H 3 O + > NH 4 + > NO 3 − , coinciding with the order of their solvation free energies. Therefore, the solvation energy can be employed as a rough index for evaluating the INN ability. Overall, the consistency between the present predictions and previous experimental and theoretical observations demonstrates the combination of MD simulation and the IINT appears to be a promising approach for exploring the IIN process and understanding the microscopic mechanism of atmospheric-related ions.

Virtual Issue on Atmospheric Aerosol Research

“…New particles are generally formed via nucleation, a process in which individual molecules interact with one another until a critical cluster size is reached and particle nucleation becomes favorable . Photoassisted particle formation can be important in many cases, while heterogeneous processes can also be key drivers, as shown in detailed quantum chemical cluster calculations .…”

“…New particles are generally formed via nucleation, a process in which individual molecules interact with one another until a critical cluster size is reached and particle nucleation becomes favorable. 2 Photoassisted particle formation can be important in many cases, 3 while heterogeneous processes can also be key drivers, as shown in detailed quantum chemical cluster calculations. 4 Molecular precursors for new particle formation and secondary organic aerosol particles can involve the formation of highly oxygenated organic molecules from the oxidation of biogenic terpenes such as α-pinene, and the development of chemical mechanisms to describe this process is critical for climate predictions.…”

Study of Electron Collisions with Isoprene, 1,2-Butadiene, and Their Isomers

“…By comparing the aliphatic absorbing property of isoprene dust with the reported interstellar medium (ISM) emission spectrum, Günay et al synthesized isoprene-formed cosmic dust analogues and recommended that isoprene is a good candidate for the constituent of interstellar dust. Isoprene also acts as a precursor to globally dominant aerosols , that play a critical role in the Earth’s atmosphere . The Blue Mountains north of Sydney and the Blue Ridge Mountains of central Appalachian are examples of thickly forested places where these aerosols cause the blue haze.…”

Molecular dynamics study on the surface tension of succinic acid-water nano-aerosol droplets

“…光学特性、相态和粒径等影响其环境气候和健康效应。同时，气溶胶吸湿生长机理研究 也可为蒸汽相变凝并脱除细颗粒技术的改进和相关设备的研制提供基础科学依据 [3,4] 。 当前，气溶胶吸湿特性(即稳态时粒径和环境中水蒸气过饱和度的关系)主要采用经典 Köhler 理论进行描述，该理论将颗粒表面饱和蒸气压用拉乌尔效应和开尔文效应描述， 表面张力为开尔文项的核心参数 [5] 。 对于液体表面张力测量的常规方法包括气泡压力法、吊环法和悬滴法等。近年来， 出现了针对液滴表面张力测量的振荡液滴法和原子力显微镜法，前者通过对比液滴阻尼 振荡频率的实验和理论结果获取表面张力 [6] ；后者通过基底上液滴表面探针保持力的结 果获取表面张力 [7] ， 然而， 这些方法对纳米尺度气溶胶液滴表面张力的测量均难以奏效。 在液体表面张力的理论研究方面， Dutcher 等 [8] 提出了一个半经验模型用于预测电解质溶 液及其混合物的表面张力，其中电解质溶液的摩尔浓度从近似 0 到 1。该模型被集成到 描述气溶胶相平衡研究领域广泛使用的 E-AIM 模型 (Extended Aerosol Inorganics Model) [9] 中。 随着计算机技术的发展，分子模拟方法在气液界面结构和特性的定量描述中得到应 用。Chapela 等 [10] 用蒙特卡洛方法和分子动力学方法研究了纯 L-J 分子组成的水平气液 界面的张力，对比了两种方法得出的表面张力等热力学参量，验证了分子动力学模拟用 于求解表面张力的可行性。Blokhuis 等 [11] 对 Chapela 等 [10] 表面张力计算方法进行改进， 通过增加尾部修正项，获得了与宏观表面张力值更为接近的模拟结果。Chen 等 [12] 利用 3 分子动力学方法模拟了由不同水分子模型(TIP3P, SPC, SPC/E, TIP4P, TIP5P)构成的水 平液面在温度为 275-350 K 条件下的表面张力，发现 SPC/E 模型得到的结果与实验值吻 合最好。 Wang 等 [13] 基于分子动力学方法定量描述了 NaCl 溶液由极稀到高度过饱和时的 表面张力。Sun 等 [14] 研究了包含不同种类卤化钠(NaF，NaCl，NaBr，NaI)纳米液滴 的表面张力。Liu 等 [15] 研究了由不同种类离子和水分子构成团簇的表面张力及其对离子 诱导成核自由能的影响。 表面活性成分是大气气溶胶颗粒中一类常见且具有特殊性质的成分，其来源包括化 石燃料燃烧、植物排放和大气中的气-粒反应等 [16] 。由于表面活性成分同时包含疏水基 和亲水基，其趋向于分布于液滴表面，同时影响表面张力和体相内组分活度。近期，课 题组基于分子动力学方法研究了包含常见表面活性成分气溶胶吸湿生长后的结构和界 面微观特性 [17] 。本文在课题组前期研究的基础上，对含表面活性物质(丁二酸，SA) 气溶胶颗粒吸湿形成稳定液滴后的表面张力进行模拟计算，重点探究温度、粒径和丁二 酸浓度对表面张力的影响机制。 模拟过程中使用 Nosé -Hoover 热浴控制模拟体系的温度 [18,19] 。本文的分子模拟工作基于 LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) 开源程序 [20] 开展。 在模拟体系中， 丁二酸采用 OPLSAA 力场参数 [21] ， 水分子选用 SPC/E 水分子模型， 该水分子模型已被成功应用于包含无机盐或有机物液滴中水分的蒸发和凝结过程研究 [22,23] 。为了减少边界条件对模拟体系的影响，三个方向均采用周期性边界条件。体系中…”