Mirrielees Jessica A, Kirpes Rachel M, Haas Savannah M, Rauschenberg Carlton D, Matrai Patricia A, Remenapp Allison, Boschi Vanessa L, Grannas Amanda M, Pratt Kerri A, Ault Andrew P
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States.
Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085, United States.
ACS Meas Sci Au. 2022 Dec 21;2(6):605-619. doi: 10.1021/acsmeasuresciau.2c00041. Epub 2022 Sep 2.
Sea spray aerosol (SSA) is one of the largest global sources of atmospheric aerosol, but little is known about SSA generated in coastal regions with salinity gradients near estuaries and river outflows. SSA particles are chemically complex with substantial particle-to-particle variability due to changes in water temperature, salinity, and biological activity. In previous studies, the ability to resolve the aerosol composition to the level of individual particles has proven necessary for the accurate parameterization of the direct and indirect aerosol effects; therefore, measurements of individual SSA particles are needed for the characterization of this large source of atmospheric aerosol. An integrated analytical measurement approach is required to probe the chemical composition of individual SSA particles. By combining complementary vibrational microspectroscopic (Raman and optical photothermal infrared, O-PTIR) measurements with elemental information from computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM-EDX), we gained unique insights into the individual particle chemical composition and morphology. Herein, we analyzed particles from four experiments on laboratory-based SSA production using coastal seawater collected in January 2018 from the Gulf of Maine. Individual salt particles were enriched in organics compared to that in natural seawater, both with and without added microalgal filtrate, with greater enrichment observed for smaller particle sizes, as evidenced by higher carbon/sodium ratios. Functional group analysis was carried out using the Raman and infrared spectra collected from individual SSA particles. Additionally, the Raman spectra were compared with a library of Raman spectra consisting of marine-derived organic compounds. Saccharides, followed by fatty acids, were the dominant components of the organic coatings surrounding the salt cores of these particles. This combined Raman, infrared, and X-ray spectroscopic approach will enable further understanding of the factors determining the individual particle composition, which is important for understanding the impacts of SSA produced within estuaries and river outflows, as well as areas of snow and ice melt.
海喷雾气溶胶（SSA）是全球大气气溶胶的最大来源之一，但对于在河口和河流流出附近具有盐度梯度的沿海地区产生的SSA却知之甚少。由于水温、盐度和生物活性的变化，SSA颗粒在化学上很复杂，颗粒间存在很大差异。在先前的研究中，已证明将气溶胶成分解析到单个颗粒水平的能力对于准确参数化气溶胶的直接和间接效应是必要的；因此，需要对单个SSA颗粒进行测量，以表征这一巨大的大气气溶胶来源。需要一种综合分析测量方法来探测单个SSA颗粒的化学成分。通过将互补的振动显微光谱（拉曼光谱和光热红外光谱，O-PTIR）测量与来自计算机控制扫描电子显微镜和能量色散X射线分析（CCSEM-EDX）的元素信息相结合，我们对单个颗粒的化学成分和形态有了独特的见解。在此，我们分析了2018年1月从缅因湾采集的沿海海水进行的四项基于实验室的SSA生成实验中的颗粒。与天然海水相比，无论是否添加微藻滤液，单个盐颗粒中的有机物都有所富集，粒径越小富集程度越高，碳/钠比更高就证明了这一点。使用从单个SSA颗粒收集的拉曼光谱和红外光谱进行官能团分析。此外，将拉曼光谱与由海洋衍生有机化合物组成的拉曼光谱库进行了比较。糖类，其次是脂肪酸，是这些颗粒盐核周围有机涂层的主要成分。这种拉曼光谱、红外光谱和X射线光谱相结合的方法将有助于进一步了解决定单个颗粒组成的因素，这对于理解河口和河流流出区域以及冰雪融化区域产生的SSA的影响非常重要。
