Estillore Armando D, Morris Holly S, Or Victor W, Lee Hansol D, Alves Michael R, Marciano Meagan A, Laskina Olga, Qin Zhen, Tivanski Alexei V, Grassian Vicki H
Department of Chemistry and Biochemistry, University of California San Diego, 3030 Urey Hall Addition, 9500 Gilman Dr, Mail Code: 0314, La Jolla, CA 92093, USA.
Phys Chem Chem Phys. 2017 Aug 9;19(31):21101-21111. doi: 10.1039/c7cp04051b.
Individual airborne sea spray aerosol (SSA) particles show diversity in their morphologies and water uptake properties that are highly dependent on the biological, chemical, and physical processes within the sea subsurface and the sea surface microlayer. In this study, hygroscopicity data for model systems of organic compounds of marine origin mixed with NaCl are compared to data for authentic SSA samples collected in an ocean-atmosphere facility providing insights into the SSA particle growth, phase transitions and interactions with water vapor in the atmosphere. In particular, we combine single particle morphology analyses using atomic force microscopy (AFM) with hygroscopic growth measurements in order to provide important insights into particle hygroscopicity and the surface microstructure. For model systems, a range of simple and complex carbohydrates were studied including glucose, maltose, sucrose, laminarin, sodium alginate, and lipopolysaccharides. The measured hygroscopic growth was compared with predictions from the Extended-Aerosol Inorganics Model (E-AIM). It is shown here that the E-AIM model describes well the deliquescence transition and hygroscopic growth at low mass ratios but not as well for high ratios, most likely due to a high organic volume fraction. AFM imaging reveals that the equilibrium morphology of these single-component organic particles is amorphous. When NaCl is mixed with the organics, the particles adopt a core-shell morphology with a cubic NaCl core and the organics forming a shell similar to what is observed for the authentic SSA samples. The observation of such core-shell morphologies is found to be highly dependent on the salt to organic ratio and varies depending on the nature and solubility of the organic component. Additionally, single particle organic volume fraction AFM analysis of NaCl : glucose and NaCl : laminarin mixtures shows that the ratio of salt to organics in solution does not correspond exactly for individual particles - showing diversity within the ensemble of particles produced even for a simple two component system.
单个空气传播的海喷雾气溶胶（SSA）颗粒在形态和吸湿特性上表现出多样性，这高度依赖于海洋次表层和海面微层内的生物、化学和物理过程。在本研究中，将海洋来源有机化合物与氯化钠混合的模型系统的吸湿数据与在海洋 - 大气设施中收集的真实SSA样本的数据进行比较，以深入了解SSA颗粒的生长、相变以及与大气中水蒸气的相互作用。特别是，我们将使用原子力显微镜（AFM）的单颗粒形态分析与吸湿生长测量相结合，以便深入了解颗粒的吸湿性和表面微观结构。对于模型系统，研究了一系列简单和复杂的碳水化合物，包括葡萄糖、麦芽糖、蔗糖、海带多糖、海藻酸钠和脂多糖。将测量的吸湿生长与扩展气溶胶无机物模型（E - AIM）的预测结果进行比较。结果表明，E - AIM模型在低质量比下能很好地描述潮解转变和吸湿生长，但在高质量比下则不然，这很可能是由于有机物体积分数较高。AFM成像显示这些单组分有机颗粒的平衡形态是无定形的。当氯化钠与有机物混合时，颗粒呈现核壳形态，有一个立方氯化钠核心，有机物形成外壳，类似于在真实SSA样本中观察到的情况。发现这种核壳形态的观察结果高度依赖于盐与有机物质的比例，并且根据有机成分的性质和溶解度而变化。此外，对氯化钠∶葡萄糖和氯化钠∶海带多糖混合物的单颗粒有机物体积分数AFM分析表明，溶液中盐与有机物的比例对于单个颗粒并不完全对应——即使对于一个简单的二元系统，在产生的颗粒集合中也显示出多样性。
