scholarly journals An experimental study on light scattering matrices for Chinese loess dust with different particle size distributions

2019 ◽  
Author(s):  
Jia Liu ◽  
Qixing Zhang ◽  
Jinjun Wang ◽  
Yongming Zhang
Keyword(s):  
Particle Size ◽  
Refractive Index ◽  
Light Scattering ◽  
Dust Particles ◽  
Size Distributions ◽  
Long Distance ◽  
Microscopic Appearance ◽  
Chinese Loess ◽  
Two Samples ◽  
Scattering Matrices

Abstract. Mineral dust suspended in the atmosphere has significant effects on radiative balance and climate change. Chinese Loess Plateau (CLP) is generally considered as a main sources of Asian dust aerosol. After being lifted by wind, dust particles with various size distributions can be transported for different distances. In this study, original loess sample was collected from Luochuan, which is centrally located at CLP, and two samples with different size distributions were obtained after then. Pristine loess was used to represent dust that only affect source regions, part of pristine loess was milled to finer milled loess that can be transported for long distance. Light scattering matrices for these two samples were measured at 532 nm wavelength from 5° to 160° angles. Particle size distribution, refractive index, chemical component, and microscopic appearance were also measured for auxiliary analyses. Results showed that discrepancies in angular behaviours of matrix elements for pristine loess and milled loess cannot be ignored. Given that the effective radii of these two loess samples differ by more than 20 times, it is reasonable to conclude that the difference in size distributions plays a major role in leading to different matrices, while refractive index and micro structure have relatively small impacts. Analyses of numerical simulation results about irregular particles also variety this conclusion. At last, synthetic scattering matrices for both pristine loess and milled loess were calculated over 0°–180°, and the previous average scattering matrix for loess dust was updated.

scholarly journals An experimental study on light scattering matrices for Chinese loess dust with different particle size distributions

2020 ◽  
Vol 13 (8) ◽  
pp. 4097-4109
Author(s):  
Jia Liu ◽  
Qixing Zhang ◽  
Yinuo Huo ◽  
Jinjun Wang ◽  
Yongming Zhang
Keyword(s):  
Particle Size ◽  
Refractive Index ◽  
Light Scattering ◽  
Scattering Matrix ◽  
Dust Aerosol ◽  
Dust Particles ◽  
Size Distributions ◽  
Chinese Loess ◽  
Two Samples ◽  
Scattering Matrices

Abstract. Mineral dust suspended in the atmosphere has significant effects on radiative balance and climate change. The Chinese Loess Plateau (CLP) is generally considered one of the main sources of Asian dust aerosol. After being lifted by wind, dust particles with various size distributions can be transported over different distances. In this study, an original loess sample was collected from Luochuan, which is centrally located on the CLP, and two samples with different size distributions were obtained afterwards. “Pristine loess” was used to represent dust that only affects source regions, part of pristine loess was milled to finer “milled loess” that can be transported over long distances. Light scattering matrices for these two samples were measured at 532 nm wavelength from 5 to 175∘ angles. Particle size distribution, refractive index, chemical component, and microscopic appearance were also characterized for auxiliary analyses. Experimental results showed that there are obvious discrepancies in angular behaviors of matrix elements for pristine loess and milled loess, and these discrepancies are different from those for other kinds of dust with distinct size distributions. Given that the effective radii of these two loess samples differ by more than 20 times, it is reasonable to conclude that the difference in size distributions plays a major role in leading to different matrices, while differences in refractive index and microstructure have relatively small contributions. Qualitative analyses of numerical simulation results of irregular particles also validate this conclusion. Gaussian spheres may be promising morphological models for simulating the scattering matrix of loess but need further quantitative verification. Finally, synthetic scattering matrices for both pristine loess and milled loess were constructed over 0–180∘, and the previous average scattering matrix for loess dust was updated. This study presents measurement results of Chinese loess dust and an updated average scattering matrix for loess, which are useful for validating existing models, developing more advanced models for optical simulations of loess dust, and helping to improve retrieval accuracy of dust aerosol properties over both source and downwind areas.

scholarly journals Observations of Saharan dust microphysical and optical properties from the Eastern Atlantic during NAMMA airborne field campaign

2011 ◽  
Vol 11 (2) ◽  
pp. 723-740 ◽  
Author(s):  
G. Chen ◽  
L. D. Ziemba ◽  
D. A. Chu ◽  
K. L. Thornhill ◽  
G. L. Schuster ◽  
...  
Keyword(s):  
Particle Size ◽  
Optical Properties ◽  
Dust Particle ◽  
Saharan Dust ◽  
Dust Particles ◽  
Small Range ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Field Campaign ◽  
Sahara Dust

Abstract. As part of the international project entitled "African Monsoon Multidisciplinary Analysis (AMMA)", NAMMA (NASA AMMA) aimed to gain a better understanding of the relationship between the African Easterly Waves (AEWs), the Sahara Air Layer (SAL), and tropical cyclogenesis. The NAMMA airborne field campaign was based out of the Cape Verde Islands during the peak of the hurricane season, i.e., August and September 2006. Multiple Sahara dust layers were sampled during 62 encounters in the eastern portion of the hurricane main development region, covering both the eastern North Atlantic Ocean and the western Saharan desert (i.e., 5–22° N and 10–35° W). The centers of these layers were located at altitudes between 1.5 and 3.3 km and the layer thickness ranged from 0.5 to 3 km. Detailed dust microphysical and optical properties were characterized using a suite of in-situ instruments aboard the NASA DC-8 that included a particle counter, an Ultra-High Sensitivity Aerosol Spectrometer, an Aerodynamic Particle Sizer, a nephelometer, and a Particle Soot Absorption Photometer. The NAAMA sampling inlet has a size cut (i.e., 50% transmission efficiency size) of approximately 4 μm in diameter for dust particles, which limits the representativeness of the NAMMA observational findings. The NAMMA dust observations showed relatively low particle number densities, ranging from 268 to 461 cm−3, but highly elevated volume density with an average at 45 μm3 cm−3. NAMMA dust particle size distributions can be well represented by tri-modal lognormal regressions. The estimated volume median diameter (VMD) is averaged at 2.1 μm with a small range of variation regardless of the vertical and geographical sampling locations. The Ångström Exponent assessments exhibited strong wavelength dependence for absorption but a weak one for scattering. The single scattering albedo was estimated at 0.97 ± 0.02. The imaginary part of the refractive index for Sahara dust was estimated at 0.0022, with a range from 0.0015 to 0.0044. Closure analysis showed that observed scattering coefficients are highly correlated with those calculated from spherical Mie-Theory and observed dust particle size distributions. These values are generally consistent with literature values reported from studies with similar particle sampling size range.

scholarly journals Elliptical Polarization by Light Scattering by Submicron Spheroids

1973 ◽  
Vol 52 ◽  
pp. 131-137
Author(s):  
Th. Schmidt
Keyword(s):  
Refractive Index ◽  
Light Scattering ◽  
Axial Ratio ◽  
Incident Radiation ◽  
Dust Particles ◽  
Elliptical Polarization ◽  
Polarized Radiation

Calculations have been carried out of single light scattering by Rayleigh type spheroidal dust particles. It can be shown that elliptical polarized radiation with e = v/p ≈ 0.15 can be produced from unpolarized incident radiation, in the case of dirty quartz particles with a refractive index m = 1.54 ± 0.4i and a geometrical axial ratio c: a ≈ 1:2.

scholarly journals Dust Particle Size Distributions during Spring in Yinchuan, China

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Jiangfeng Shao ◽  
Jiandong Mao
Keyword(s):  
Particle Size ◽  
Wind Speed ◽  
Dust Particle ◽  
Dust Storm ◽  
Fine Particles ◽  
Dust Particles ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Mass Distributions ◽  
Mass Size

Dust particle size distributions in Yinchuan, China, were measured during March and April 2014, using APS-3321 sampler. The distributions were measured under different dust conditions (background, floating dust, blowing dust, and dust storm) and statistical analyses were performed. The results showed that, under different dust conditions, the instantaneous number concentrations of dust particles differed widely. For example, during blowing sand and dust storm conditions, instantaneous dust particles concentrations varied substantially, while, under floating dust conditions, concentration differences were relatively small. The average dust particles size distributions were unimodal under all dust conditions, but the average surface area and mass size distributions were all bimodal. These distributions had peaks in different locations under different dust conditions. Under different dust conditions, wind speed and humidity were very important factors for particles size distributions. With increasing wind speed and decreasing humidity, fine particles were dominant in the atmosphere and the number and mass distributions of the coarse particles were indicative of long-range transport from surrounding deserts. Different dust conditions had different influences on PM1, PM2.5, and PM10concentrations.

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