Backscattering Properties Of Dust And Soot-contaminated Dust Aerosols

Aerosols are important components of the Earths atmosphere and exert significant effects on atmospheric radiative transfer,and further on the weather and climate system.To study the radiative impact of aerosols,an accurate knowledge of the optical properties of aerosols should be first obtained.In addition,Light detection and ranging(LiDAR)signal interpretation related to aerosol typing requires reliable knowledge of the optical backscattering properties of atmospheric particles.However,the diversity and complexity of aerosols make the aerosol optical property study a nontrivial research subject.To circumvent the difficulty,this thesis adopted a simplified aerosol model for studying the optical properties of aerosols and investigated its effeteness in modeling the LiDAR returning signals from atmospheric aerosols.Dust and soot are two major components of atmospheric aerosols.Dust aerosol accounts for about 50%of atmospheric aerosol mass.The main source of soot aerosol is incomplete combustion of fossil energy and biological fuel.Dust and soot can mix during aerosol transport process,which causes further complexity on assessing their impacts on radiative transfer.In this study,super-spheroids with constrained parameters are used to model dust particle geometry.In contrast to conventional spheroidal model,the super-spheroidal model has additional geometric freedom and can model the concavity of dust particle surface.A fractal geometry is used to model soot particles and soot-contaminated dust is modeled by super-spheroids with soot adhesions.In LiDAR remote sensing,the microphysical properties of aerosols are obtained from derived backscattering ratios(depolarization ratio,lidar ratio,and color ratio).With defined super-spheroidal dust and fractal soot models,the invariant imbedding T-matrix method was employed to calculate the depolarization,color,and LiDAR ratios of transported dust and soot-contaminated dust at triple LiDAR wavelengths(0.355,0.532,and 1.064 ?m,respectively).Furthermore,the results based on the dust-soot aggregate model were compared with their counterparts obtained by assuming a mixture of dust and soot without interactions.It was found that adhesion has a large impact on the depolarization and LiDAR ratios.To further assess the applicability of the aforementioned dust and contaminated dust models,the theoretical results are discussed in comparison with Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation(CALIPSO)observations,laboratory measurements and various ground-based LiDAR observations.It was found that the depolarization ratio,color ratio,and LiDAR ratio values of pure dust and polluted dust were in good agreement with the theoretical simulation results.These findings confirmed the reasonability of the dust and soot-contaminated dust models for future applications in atmospheric radiative transfer.