Wang Jing, Niu Shengjie, Xu Dan
Appl Opt. 2018 Feb 10;57(5):992-1004. doi: 10.1364/AO.57.000992.
In this study, aerosol optical depth (AOD) and extinction Ångström exponent (EAE) are derived from ground-based sunphotometer observations between 2007 and 2014 at urban sites of Nanjing over the Yangtze River Delta. In addition, the present study aims to investigate aerosol light-absorbing properties such as single-scattering albedo (SSA), absorption Ångström exponent (AAE), and the aerosol-absorbing optical depth (AAOD). The retrieval of aerosol properties is compared with AERONET inversion products. The results demonstrate that the retrieved AOD has a good agreement with the AERONET Level 1.5 data, with the root mean square error being 0.068, 0.065, and 0.026 for total, fine mode, and coarse mode at 440 nm, respectively. The SSA values indicate similar accuracies in the results, which are about 0.003, -0.009, -0.008, and 0.010 different from AERONET at 440, 670, 870, and 1020 nm, respectively. The occurrence frequency of background level AOD (AOD<0.10) at 440 nm in this region is limited (1%). Monthly mean AOD, SSA, the effective radius (R), and the volume concentration at 440 nm were 0.6-1.3, 0.85-0.92, 0.24-0.40 μm, and 0.18-0.28 μm μm, respectively. The mean value of AAOD at 440 nm (AAOD) was the highest in both summer (0.095±0.041) and autumn (0.094±0.042), but was the lowest in winter (0.079±0.036). It was also noted that SSA was found to be higher during summer (0.89±0.05). The spectral variation of SSA was observed to be strongly wavelength-dependent during all seasons. The seasonal mean AAE440-870 is the highest in winter (0.86±0.41) and lowest in spring (0.49±0.29). In winter, the cumulative frequency for AAE between 1.0 and 1.2 was about 87%. The peak in the AAE distribution was close to 1.0, indicating that the aerosol column was dominated by urban-industrial aerosols and absorption species other than black carbon. Analysis of the relationship between EAE and SSA showed that the aerosol populations could be classified as "mixed" aerosol, including a mixture of both anthropogenic particles and secondary organic aerosol with highly variable sphericity fraction.
在本研究中，气溶胶光学厚度（AOD）和消光Ångström指数（EAE）是根据2007年至2014年期间在长江三角洲地区南京城市站点的地基太阳光度计观测数据得出的。此外，本研究旨在调查气溶胶的光吸收特性，如单次散射反照率（SSA）、吸收Ångström指数（AAE）和气溶胶吸收光学厚度（AAOD）。将气溶胶特性的反演结果与AERONET反演产品进行了比较。结果表明，反演得到的AOD与AERONET 1.5级数据具有良好的一致性，在440nm处，总模式、细模式和粗模式的均方根误差分别为0.068、0.065和0.026。SSA值在结果中显示出相似的精度，在440、670、870和1020nm处分别与AERONET相差约0.003、-0.009、-0.008和0.010。该地区440nm处背景水平AOD（AOD<0.10）的出现频率有限（1%）。440nm处的月平均AOD、SSA、有效半径（R）和体积浓度分别为0.6 - 1.3、0.85 - 0.92、0.24 - 0.40μm和0.18 - 0.28μm³。440nm处AAOD的平均值在夏季（0.095±0.041）和秋季（0.094±0.042）最高，但在冬季（0.079±0.036）最低。还注意到夏季的SSA较高（0.89±0.05）。观察到SSA的光谱变化在所有季节都强烈依赖于波长。季节平均AAE440 - 870在冬季最高（0.86±0.41），在春季最低（0.49±0.29）。在冬季，AAE在1.0至1.2之间的累积频率约为87%。AAE分布的峰值接近1.0，表明气溶胶柱主要由城市工业气溶胶和除黑碳以外的吸收性物种组成。对EAE和SSA之间关系的分析表明，气溶胶群体可归类为“混合”气溶胶，包括人为颗粒和具有高度可变球形度分数的二次有机气溶胶的混合物。
