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

Abstract

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.

Investigating the dependence of mineral dust depolarization on complex refractive index and size with a laboratory polarimeter at 180.0° lidar backscattering angle

“…Moreover, the complex shape of mineral dust is then accounted for. However, existing laboratory light scattering experimental setups (Glen and Brooks, 2013;Järvinen et al, 2016;Gautam et al, 2020;Liu et al, 2020;Kahnert et al, 2020;Gómez Martín et al, 2021) can only provide approximate values of the dust lidar PDR for the following reasons:…”

“…-Such apparatuses operate at near backscattering angles only (< 180.0 • ), without covering the exact lidar backscattering angle of 180.0 • . The retrieved lidar PDR is then extrapolated to 180.0 • following simplifying numerical assumptions, ignoring the complexity in the shape of mineral dust (Liu et al, 2020;Gómez Martín et al, 2021). To provide accurate values of the dust lidar PDR, such assumptions must be carefully discussed as the lidar PDR actually depends on the scattering angle in an unpredictable way, as underscored in light scattering textbooks (Bohren and Huffman, 1983;Mishchenko et al, 2002), due to the complex shape of mineral dust.…”

Analysis of Fat and Protein Content in Milk Using Laser Polarimetric Scatterometry

“…In particular, the angular dependences of the elements of the light scattering matrix (LSM) describing such a change in the of polarization state of light scattered by the dispersed medium and make it possible to determine the number and size distribution of particles, as well as to distinguish solid particles from clusters consisting of smaller particles. As follows from the literature, the LSM method, which is also called laser polarimetric scatterometry (LPS) or Mueller matrix scatterometry (MMS), can be used to analyze various mineral and bioorganic dispersed systems [5][6][7][8][9][10][11][12][13][14][15][16]. It should be noted that an attempt to empirically determine milk fat by measuring the LSM of diluted milk samples was made in [5].…”

Investigating the dependence of mineral dust depolarization on complex refractive index and size with a laboratory polarimeter at 180.0° lidar backscattering angle

“…Moreover, the complex shape of mineral dust is then accounted for. However, existing laboratory light scattering experimental set-ups (Glen and Brooks, 2013;Järvinen et al, 2016;Gautam et al, 2020;Liu et al, 2020;Kahnert et al, 2020;Gómez Martín et al, 2021) can only provide approximate values of the dust lidar 𝑃𝐷𝑅 for the following reasons:…”

“… Such apparatuses operate at near backscattering angles only (< 180.0°), without covering the exact lidar backscattering angle of 180.0°. The retrieved lidar 𝑃𝐷𝑅 is then extrapolated to 180.0° following simplifying numerical assumptions, ignoring the complexity in shape of mineral dust (Liu et al, 2020;Gómez Martín et al, 2021).…”