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

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. 10 "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 15 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. 20