A detailed characterization of the Saharan dust collected during the Fennec campaign in 2011: in situ ground-based and laboratory measurements
A detailed characterization of the Saharan dust collected during the Fennec campaign in 2011: in situ ground-based and laboratory measurements
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DOI：
10.5194/acp-18-1023-2018
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发表时间：
2017-06
影响因子：
6.3
通讯作者：
A. Rocha-Lima;J. Martins;L. Remer;M. Todd;J. H. Marsham;S. Engelstaedter;C. Ryder;C. Cavazos-Guerra;P. Artaxo;P. Colarco;R. Washington
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文献类型：
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作者：
A. Rocha-Lima;J. Martins;L. Remer;M. Todd;J. H. Marsham;S. Engelstaedter;C. Ryder;C. Cavazos-Guerra;P. Artaxo;P. Colarco;R. Washington
摘要。每年都有数百万吨的矿物粉尘被风从干旱的地表吹起，运送到全球各地。矿物粉尘的物理和化学性质需要更好地约束遥感观测，对了解粉尘大气过程具有根本重要性。2011年在撒哈拉中部的Fennec行动期间获得了地面现场测量和撒哈拉沙尘的现场过滤收集。本文介绍了在活动最后阶段实时测量的撒哈拉沙尘的吸收和散射系数以及单散射反照率（SSA）的结果，以及随后对分别在阿尔及利亚和毛里塔尼亚两个重叠站点SS1和SS2收集的沙尘样品的实验室分析。将样品带到实验室，在紫外（UV）到近红外（NIR）波长范围内获得样品的尺寸和纵横比分布、平均化学成分、光谱质量吸收效率和光谱虚折射率。在阿尔及利亚的SS1，在运动期间散射系数的时间序列显示沙尘事件超过3500 Mm−1，在670 nm处观测到相对较高的平均SSA为0.995。实验室结果表明，在两个位置的细颗粒尺寸分布（颗粒直径为5µm，模直径为2-3µm）中，折射率Im(m)的虚部具有弓形的光谱依赖性，在紫外和短波红外中吸收增加。然而，在阿尔及利亚的混合粒径分布（粒径为10µm，模态直径为4µm）中没有观察到相同的特征。在350-2500 nm的波长范围内，在阿尔及利亚收集的灰尘中发现的Im(m)范围为0.011至0.001i，在毛里塔尼亚收集的灰尘中发现的Im(m)范围为0.008至0.002i。从EDXRF测量中观察到，在阿尔及利亚和毛里塔尼亚的重叠地点收集的灰尘的平均元素组成以及细粒度和混合粒度分布之间存在差异，尽管这些差异不能用于解释样品之间的光学性质变化。最后，在毛里塔尼亚的超级站点收集的一些样品中发现了直径通常大于10 μ m的低密度颗粒，但在阿尔及利亚没有观察到这些低密度颗粒。
Abstract. Millions of tons of mineral dust are lifted by the wind from arid surfaces and transported around the globe every year. The physical and chemical properties of the mineral dust are needed to better constrain remote sensing observations and are of fundamental importance for the understanding of dust atmospheric processes. Ground-based in situ measurements and in situ filter collection of Saharan dust were obtained during the Fennec campaign in the central Sahara in 2011. This paper presents results of the absorption and scattering coefficients, and hence single scattering albedo (SSA), of the Saharan dust measured in real time during the last period of the campaign and subsequent laboratory analysis of the dust samples collected in two supersites, SS1 and SS2, in Algeria and in Mauritania, respectively. The samples were taken to the laboratory, where their size and aspect ratio distributions, mean chemical composition, spectral mass absorption efficiency, and spectral imaginary refractive index were obtained from the ultraviolet (UV) to the near-infrared (NIR) wavelengths. At SS1 in Algeria, the time series of the scattering coefficients during the period of the campaign show dust events exceeding 3500 Mm −1 , and a relatively high mean SSA of 0.995 at 670 nm was observed at this site. The laboratory results show for the fine particle size distributions (particles diameter 5 µ m and mode diameter at 2–3 µ m) in both sites a spectral dependence of the imaginary part of the refractive index Im(m) with a bow-like shape, with increased absorption in UV as well as in the shortwave infrared. The same signature was not observed, however, in the mixed particle size distribution (particle diameter 10 µ m and mode diameter at 4 µ m) in Algeria. Im(m) was found to range from 0.011 to 0.001i for dust collected in Algeria and 0.008 to 0.002i for dust collected in Mauritania over the wavelength range of 350–2500 nm. Differences in the mean elemental composition of the dust collected in the supersites in Algeria and in Mauritania and between fine and mixed particle size distributions were observed from EDXRF measurements, although those differences cannot be used to explain the optical properties variability between the samples. Finally, particles with low-density typically larger than 10 µ m in diameter were found in some of the samples collected at the supersite in Mauritania, but these low-density particles were not observed in Algeria.