Morphological change of solid ammonium sulfate particles below the deliquescence relative humidity: Experimental reproduction of atmospheric sulfate particle shapes
Morphological change of solid ammonium sulfate particles below the deliquescence relative humidity: Experimental reproduction of atmospheric sulfate particle shapes
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DOI：
10.1080/02786826.2020.1864277
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发表时间：
2021-01
影响因子：
5.2
通讯作者：
Sayako Ueda
中科院分区：
文献类型：
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作者：
Sayako Ueda
摘要 含有硫酸铵的大气气溶胶在固相中有多种形态类型。实验室实验用于重现大气样本中常见的颗粒形状，以阐明影响这些不同颗粒形状的因素。在不同相对湿度（RH）条件下制备硫酸铵颗粒和草酸盐混合颗粒，并使用透射电子显微镜（TEM）进行观察。从水溶液生成后使用扩散干燥器干燥的大多数硫酸铵颗粒是球形或球形单元簇。然而，在大气压下将 TEM 样品暴露于 59% RH 和 75% RH 后，一些颗粒变成以平行直线作为颗粒周长的圆矩形形状。在 59% RH 和 75% RH 下，从球形变为圆形矩形的颗粒数分数在 3 小时时分别为 6% 和 52%，在 1 天时分别为 18% 和 66%。实验过程中的形态变化表明硫酸铵结晶发生在亚稳态相对湿度下。与草酸盐共存的硫酸铵也发现了圆形矩形的形态变化。这些结果表明，球形或复杂形状的含硫酸盐气溶胶可以根据颗粒经历的相对湿度条件逐渐改变为具有更规则结构的形状。在大气气溶胶样品中经常发现球形和圆矩形形状的硫酸盐颗粒。这项研究中发现的硫酸铵的形态变化将有助于推断大气颗粒的光学特性和固体颗粒表面的热力学过程。
Abstract Atmospheric aerosols containing ammonium sulfate have several morphological types in the solid phase. Laboratory experiments were used to reproduce the particle shapes commonly found in atmospheric samples to elucidate factors affecting these different particle shapes. Ammonium sulfate particles and mixed particles with oxalate were prepared under different relative humidity (RH) conditions and were observed using transmission electron microscopy (TEM). Most ammonium sulfate particles dried using a diffusion dryer after generation from aqueous solution were spherical or clusters of spherical units. However, after exposure of the TEM samples to 59% RH and 75% RH at atmospheric pressure, some particles changed to a rotundate-rectangular shape with parallel straight lines as the particle perimeter. Number fractions of particles that had changed to rotundate-rectangular shape from a spherical shape at 59% RH and 75% RH were, respectively, 6% and 52% at 3 h, and 18% and 66% at 1 day. Morphological changes during the experiment suggest that ammonium sulfate crystallization occurred under metastable RH. Morphological changes to rotundate-rectangular shapes were also found for ammonium sulfate co-existing with oxalate. These results indicate that spherical or complexly shaped sulfate-containing aerosols can change gradually to shapes having more regular structures according to a particle’s experienced RH condition. Both spherical and rotundate-rectangular shapes of sulfate particles have often been found in atmospheric aerosol samples. The morphological change of ammonium sulfate found in this study will be useful to infer the optical properties of atmospheric particles and the thermodynamic process on a solid particle surface.