Fractal parameters of individual soot particles determined using electron tomography: Implications for optical properties
Fractal parameters of individual soot particles determined using electron tomography: Implications for optical properties
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DOI：
10.1029/2006jd008296
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发表时间：
2007-07-19
影响因子：
4.4
通讯作者：
Buseck, Peter R.
中科院分区：
文献类型：
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作者：
Adachi, Kouji;Chung, Serena H.;Buseck, Peter R.
烟尘颗粒的形态既复杂又重要。它们影响烟尘的大气寿命、全球分布和气候影响。颗粒可能具有复杂的几何形状，具有重叠的突出部分和孔隙，这很难从用于研究它们的传统技术中推断出来。我们使用电子断层扫描和透射电子显微镜（TEM）来确定三维（3D）特性，如分形维数（D-f）、旋转半径（R-g）、体积(V)、表面积（a (s)）和结构系数（k(a)），这些特性来自亚洲粉尘（AD）事件和美国交通源的环境空气中的单个烟灰颗粒。Df的中值分别为2.4和2.2，Rg的中值分别为274和251 nm， As/V的中值分别为9.2和13.7 × 10(7) m(-1)， ka的中值分别为0.67和0.71。相应的参数，当从二维投影（如TEM图像）计算时，相当不精确，而且通常是错误的。不像其他方法已经被用来推导分形参数，我们的方法适用于任何D-f粒子。利用三维数据，我们估计我们的AD和交通烟尘颗粒的质量归一化散射截面分别比未聚集球体的散射截面大15倍和30倍，这是全球模式中估计辐射强迫的假设形状。精确的三维信息可以用来计算更精确的光学性质，这对于估计直接辐射强迫和提高我们对烟灰气候影响的理解非常重要。
The morphologies of soot particles are both complex and important. They influence soot atmospheric lifetimes, global distributions, and climate impacts. Particles can have complex geometries with overlapping projecting parts and pores that are difficult to infer from the conventional techniques used to study them. We used electron tomography with a transmission electron microscope (TEM) to determine three-dimensional (3D) properties such as fractal dimension (D-f), radius of gyration (R-g), volume (V), surface area (A(s)), and structural coefficient (k(a)) for individual soot particles from the ambient air of an Asian dust ( AD) episode and from a U. S. traffic source. The respective median values of Df are 2.4 and 2.2, of Rg are 274 and 251 nm, of As/V are 9.2 and 13.7x10(7) m(-1), and of ka are 0.67 and 0.71. The corresponding parameters, when calculated from 2D projections such as TEM images, are considerably less precise and commonly erroneous. Unlike other methods that have been used to derive fractal parameters, our method is applicable to particles of any D-f. Using the 3D data, we estimate that mass-normalized scattering cross sections of our AD and traffic soot particles are respectively about 15 and 30 times greater than those of unaggregated spheres, which is the shape assumed in global models to estimate radiative forcing. Accurate 3D information can be used to compute more precise optical properties, which are important for estimating direct radiative forcing and improving our understanding of the climate impact of soot.