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Organic Enrichment, Physical Phase State, and Surface Tension Depression of Nascent Core–Shell Sea Spray Aerosols during Two Phytoplankton Blooms
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2020-03-03 , DOI: 10.1021/acsearthspacechem.0c00032
Hansol D. Lee 1 , Holly S. Morris 1 , Olga Laskina 1 , Camille M. Sultana 2 , Christopher Lee 3 , Thilina Jayarathne 1 , Joshua L. Cox 2 , Xiaofei Wang 2 , Elias S. Hasenecz 1 , Paul J. DeMott 4 , Timothy H. Bertram 5 , Christopher D. Cappa 6 , Elizabeth A. Stone 1 , Kimberly A. Prather 2, 3, 7 , Vicki H. Grassian 2, 3 , Alexei V. Tivanski 1
Affiliation  

Sea spray aerosols (SSAs) affect the Earth’s climate directly by scattering solar radiation and indirectly by acting as ice and cloud condensation nuclei. The relative magnitude of these effects remains uncertain, in part, from substantial compositional and morphological variability between individual particles. Here, the evolving heterogeneity within populations of primary SSAs produced from wave breaking of natural seawater within a wave flume is investigated. Over the course of the study, two successive phytoplankton blooms were induced in the seawater. The morphology, organic volume fraction, hygroscopicity, phase state, and surface tension of individual SSAs collected via deposition on a substrate were characterized using atomic force microscopy. Particles between ca. 0.3 and 1 μm in volume equivalent diameter displayed a distinctive morphology revealing an inorganic core coated with an organic shell. The inferred organic volume fraction was the largest at the peak of the first bloom. The corresponding shell thicknesses ranged from 21 to 40 nm at 20% relative humidity (RH). The organic shell phase state of the majority of the particles during both blooms was semisolid at 20% and 60% RH. At 20% RH, a minor fraction of the organic shells behaved as a solid, while at 60% RH some behaved as liquids during the first bloom. Similar results were evident at 20% RH for the second bloom but with no observed liquid particles at 60% RH. The thick, semisolid organic coatings could potentially reduce atmospheric water and gas uptake efficiencies onto SSAs at lower RH, along with the potential for ice nucleating activity. However, at 80% RH, the SSAs deliquesced and exhibited liquid-like behavior with surface tension values measured over individual particles of 41–87 mN m–1, demonstrating high particle-to-particle variability. The suppressed surface tension at 80% RH relative to pure water is attributed to the high concentrations of surface-active organic compounds, potentially further limiting the diffusion rate of gas molecules through the interface.

中文翻译:

两次浮游植物开花过程中新生的核-壳海喷雾气溶胶的有机富集,物理相态和表面张力降低

海水喷雾气溶胶(SSA)通过散射太阳辐射直接影响地球的气候,并通过充当冰云凝结核间接地影响地球的气候。这些影响的相对大小仍然不确定,部分原因是单个颗粒之间的实质组成和形态变异。在此,研究了由波浪槽内的天然海水的波浪破碎产生的初级SSA种群内部不断演变的异质性。在研究过程中,在海水中诱发了两次连续的浮游植物水华。使用原子力显微镜对通过沉积在基材上收集的各个SSA的形态,有机体积分数,吸湿性,相态和表面张力进行了表征。大约之间的粒子。0。体积当量直径为3和1μm时显示出独特的形态,揭示了涂有有机壳的无机核。推断的有机物体积分数在第一次开花的高峰期最大。在20%的相对湿度(RH)下,相应的外壳厚度范围为21到40 nm。在两次开花期间,大多数颗粒的有机壳相状态在RH为20%和60%时均为半固态。在相对湿度20%时,有机壳中的一小部分表现为固体,而在相对湿度60%时,一些有机壳在初次开花时表现为液体。对于第二次起霜,在20%RH下有相似的结果,但在60%RH下没有观察到液体颗粒。较厚的半固体有机涂层可能会降低相对湿度较低时,SSA上的大气水和气体吸收效率,同时可能降低冰核活性。–1,表明粒子间的高可变性。相对于纯水,在80%RH时抑制的表面张力归因于高浓度的表面活性有机化合物,有可能进一步限制气体分子通过界面的扩散速率。
更新日期:2020-04-23
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