Raman microspectroscopy and vibrational sum frequency generation spectroscopy as probes of the bulk and surface compositions of size-resolved sea spray aerosol particles
Raman microspectroscopy and vibrational sum frequency generation spectroscopy as probes of the bulk and surface compositions of size-resolved sea spray aerosol particles
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DOI：
10.1039/c3cp43899f
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发表时间：
2013-01-01
影响因子：
3.3
通讯作者：
Grassian, Vicki H.
中科院分区：
文献类型：
--
作者：
Ault, Andrew P.;Zhao, Defeng;Grassian, Vicki H.
海洋喷雾气溶胶（SSA）是大气中最大的气溶胶成分之一。SSA在影响气候方面发挥着重要作用;然而，由于整体化学复杂性，对总体影响仍然知之甚少。SSA由无机和有机成分的混合物组成，其比例随颗粒大小和海水成分的变化而变化。在这项研究中，新生SSA颗粒使用破碎波产生，从而产生代表开阔海洋的组成和大小。单个SSA颗粒的组成在尺寸范围内从约. 0.15到10 μ m使用拉曼显微光谱测量，而尺寸分辨颗粒的集合的界面组成通过和频发生（SFG）探测。单粒子的拉曼光谱在980 - 1030 cm（-1）区域内有与硫酸根阴离子的对称伸缩相关的谱带，在2800 - 3000 cm（-1）区域内有与碳氢伸缩相关的谱带，在3200-3700 cm（-1）区域内有与水的氧-氢伸缩相关的谱带。这些功能的相对强度表现出强烈的依赖于颗粒大小。特别地，亚微米颗粒与超微米颗粒相比表现出更大量的有机物质。然而，对于均匀SSA颗粒（即没有固体夹杂物的颗粒）的外表面，以及混合相颗粒的界面，亚微米和超微米颗粒的脂肪族C-H伸缩区域中存在强烈的SFG响应。这一发现表明，存在于超微米颗粒中的有机材料主要存在于界面处。在SFG光谱中亚甲基的贡献表明无序的烷基链的存在下，相反，人们可能期望的海盐颗粒上的表面活性剂层。在C-H伸缩区的峰值频率和相对强度的变化被认为是一些粒子后，添加细菌，浮游植物，和生长介质的海水。这项研究为SSA颗粒的体积和表面组成提供了新的见解，并代表了我们对这种全球丰富的气溶胶的理解向前迈进了一步。它还提供了深入了解SSA的模型系统的发展，可以更准确地代表在表面的有机层。
Sea spray aerosol (SSA) represents one of the largest aerosol components in our atmosphere. SSA plays a major role in influencing climate; however the overall impacts remain poorly understood due to the overall chemical complexity. SSA is comprised of a mixture of inorganic and organic components in varying proportions that change as a function of particle size and seawater composition. In this study, nascent SSA particles were produced using breaking waves, resulting in compositions and sizes representative of the open ocean. The composition of individual SSA particles ranging in size from ca. 0.15 to 10 mu m is measured using Raman microspectroscopy, while the interfacial composition of collections of size-resolved particles is probed by sum frequency generation (SFG). Raman spectra of single particles have bands in the 980 to 1030 cm(-1) region associated with the symmetric stretch of the sulfate anion, the 2800 to 3000 cm(-1) region associated with carbon-hydrogen stretches, and from 3200-3700 cm(-1) associated with the oxygen-hydrogen stretches of water. The relative intensities of these features showed a strong dependence on particle size. In particular, submicrometer particles exhibited a larger amount of organic matter compared to supermicrometer particles. However, for external surfaces of homogeneous SSA particles (i.e. particles without a solid inclusion), and also the interfaces of mixed-phase particles, there was a strong SFG response in the aliphatic C-H stretching region for both sub-and supermicrometer particles. This finding suggests that organic material present in supermicrometer particles primarily resides at the interface. The presence of methylene contributions in the SFG spectra indicated disordered alkyl chains, in contrast to what one might expect for a surfactant layer on a sea salt particle. Changes in peak frequencies and relative intensities in the C-H stretching region are seen for some particles after the addition of bacteria, phytoplankton, and growth medium to the seawater. This study provides new insights into the bulk and surface composition of SSA particles and represents a step forward in our understanding of this globally abundant aerosol. It also provides insights into the development of model systems for SSA that may more accurately represent the organic layer at the surface.