黑碳团簇及具有包覆水层混合态粒子的光学特性

Optical Properties of Soot Aggregates and Mixture Particles with Water Coatings

基于扩散限制凝聚模型仿真生成了黑碳团簇粒子和具备核-壳结构(核为黑碳团簇,壳为包覆水层)的混合态粒子,并模拟了黑碳团簇粒子的老化过程,利用团簇T矩阵方法计算并研究了粒子形态结构和包覆水层对两种粒子在550nm波长处的光学特性。分析表明,新生黑碳团簇粒子的光学特性参数与等体积球形黑碳粒子之间的差异最大,当分形维数Df为1.8时,散射截面和单次散射反照率的相对偏差分别达到61.58%和49.44%,随着黑碳团簇粒子的老化,差异逐渐减小。对于混合态粒子,忽略黑碳核的团簇结构会导致前向散射强度、散射截面、消光截面、单次散射反照率、不对称因子和F_(34)/F_(11)被低估,导致后向散射强度、吸收截面、-F_(12)/F_(11)、F_(33)/F_(11)、F_(44)/F_(11)被高估;包覆水层厚度的增加会加剧混合态粒子散射矩阵中元素随散射角的振荡程度,且忽略黑碳核或球形黑碳核假设所引起的光学特性参数相对偏差呈逐渐减小的趋势。该工作有助于进一步减小黑碳气溶胶辐射强迫估算误差。

Based on the diffusion-limited aggregation model, the aggregated soot and its mixture particles with water coating are generated. The aging process of soot aggregates is simulated. The effects of particle morphology and water coating on the optical properties of the two kinds of particles at the wavelength of 550 nm are studied by the cluster T-matrix method. The results show that the difference of optical property parameters between the freshly generated soot aggregate and the spherical soot with the same volume is larger than the difference between the aged soot aggregate and the spherical soot. When the fractal dimension Df is 1.8, the relative differences of scattering cross section and single scattering albedo reach 61.58% and 49.44%, respectively. As the aging process proceeds, the differences decrease. For the mixture particles, ignoring the cluster structure of the soot core can lead to underestimation of the forward scattering intensity, scattering cross section, extinction cross section, single scattering albedo, asymmetry factor, and F34/F11, and overestimation of the backward scattering intensity, absorption cross section, -F12/F11, F33/F11, and F44/F11. With the increase of the water coating thickness, the scattering matrix elements of mixtures are more turbulent with scattering angle, and the relative differences of optical property parameters caused by ignoring the soot core and the aggregated morphology of soot core are both reduced. This study has significance for decreasing the estimation error of radiative forcing estimation due to soot aerosol.