A Study On The Uncertainty In Numerical Simulation Of Dust Aerosol Light Scattering Properties

Dust aerosol,as one of the most important aerosols,plays a crucial role in the atmosphere by directly interacting with radiation,while there are significant uncertainties in determining dust optical properties to quantify radiative effects.At present,the laboratory and simulation researches on the light scattering properties of dust aerosols are very limited,and different refractive indices and size distributions have been applied in numerical studies used for model developments,aerosol retrievals,and radiative forcing simulations.This paper reveals the unique effects of uncertainties of refractive index,model geometry,and size distribution on the numerical simulation on light scattering properties of dust aerosol.First,this paper construct an optical model based on the Koch-fractal particle geometry,and a combination of the pseudospectral time domain?PSTD?method and the improved geometric-optics method?IGOM?is used to compute the light scattering properties of the optical model.The simulated results of the scattering matrices of feldspar,quartz,loess,red clay,and Lokon volcanic ash are obtained by integrals based on the measured size distributions provided by the Amsterdam–Granada Light Scattering Database?AGLSD?.The ranges of refractive indices are[1.4,2.2]for the real part and[10^-4,10^-2]for the imaginary part,and the range of aspect ratio is[0.25,4.0].By comparing the computed results with the measured data,this paper finds that both the adjustments of the refractive index and the shape parameters can cause significant changes and produce an optimization effect on the simulated results of the dust aerosols,and the optimization effect shows different characteristics with the change of the type of dust aerosols:for the samples feldspar,quartz,and loess,the scattering matrices can be effectively simulated by changing the refractive index or changing the aspect ratio of the model;for the sample red clay,more accurate results are obtained by changing the aspect ratio;for the sample Lokon,more accurate results are obtained by changing the refractive index.The uncertainty of the size distribution can affect the simulated results as well,but both its uncertainty and effect are smaller than those of refractive index and shape parameters.The uncertainties of the refractive index and the shape parameters also have significant impacts on the determinations of each other in the calculations of the scattering matrices of dust aerosols,and they have different effects on the simulated scattering matrix elements:the elements P₁₁,P₁₂,and P₂₂ are more sensitive to the changes of refractive index,while the elements P₃₃,P₄₃,and P₄₄ are more sensitive to the changes of shape parameters.The results of this paper provide experience and data for the establishment and optimization of a more accurate aerosol light scattering database.