Experimental Study On Optical Constants Of Aerosol Particles And Numerical Simulation Of Radiative Transfer

Aerosol particles are widespread in nature in forms of dust, smoke, microbes,spores, pollen and so on. Aerosol particles can not only affect human health, but alsolead to changes in weather and climate. The direct impact aerosol particles have onweather and climate is reflected in its scattering and absorption of solar shortwaveradiation and the Earth’s longwave radiation, and thus affect the radiative balance ofthe earth-atmosphere system. Therefore, the study of aerosol particle radiation is ofgreat significance to atmospheric optics, atmospheric radiation science, climatology,environmental medicine, ecology and other disciplines. In this paper, thesystematical study on radiation transfer theory and numerical method for solving inparticipating media with aerosol particles have been presented. The infrared spectraltransmittance characteristics of aerosol particles with collimated and diffuseincident irradiation are discussed. Based on transmittance of the aerosol particlesfrom experiments, the inverse model to obtain the optical constant of aerosolparticles is developed. The infrared radiative characteristics and atmosphericradiative transfer for a typical aerosol particle system, namely, cloud, are calculated.Firstly, integral equation method and the integral equation finite elementmethod are proposed to solve the radiative transfer within a two-dimensionalparticipating media. The radiation transfer caculations in the anisotropic scatteringmedia have been done for both regular and irregular enclosures. The influences ofthe scattering phase function, albedo, and the wall emissivity on the incidentradiation intensity and heat flux are studied in the dissertation. Based on the analysisof the spherical harmonics method (P1andP3), the finite difference model haspresented for the participating media with complicated anisotropic scattering.Further research has been done usingP1in conjunction with the finite elementmethod to deal with the radiative heat transfer in two-dimensional participatingmedia with regular and irregular enclosures.Secondly, A computational model of the infrared transmission characteristics ofthe aerosol particle layer with collimated and diffuse incident irradiation ispresented. On the basis ofP1approximation, MDA method has been developed forsolving the infrared transmission characteristics of the aerosol particle layer. Influencing factors (such as particle size, particle shape, particle volume fraction,particle layer thickness, the detection angle) on infrared transmission characteristicsof aerosol particle layer factors are studied in further reseach. The best infraredstealth diameter of water fog particles is obtained for the detecting waveband3-5μmand8-12μm.Based on the analysis above, a transmission model is used to obtain the opticalconstants of aerosol particles. The infrared spectral transmittance of mixed particleswhich is a mixture of different types of aerosol particles can be measured by meansof the experimental measurement. Combined with the Mie theory and K-Krelationship, the equivalent spectral optical constants of the mixed particles havebeen inversed with the measured infrared spectral transmittance. It is shown that theequivalent optical constant of the mixed particles lies between the optical constantsof each component. Comparing the inversion results with those are calculated by theeffective medium theory, certain differences exist between them which have therelationship with the volume fractions and mixed mode for each component.Furthermore, the equivalent optical constant of aerosol particles collected in Harbinarea is determined by the inverse model used in the present work. The real part ofthe equivalent optical constant of aerosol particles in Harbin area varies between1.45and1.7, and the imaginary part between0and0.3.For the typical aerosol particles-cloud, the radiative properties and infraredtransmission characteristics of water cloud and water clouds containing differenttypes of aerosol particles are studied with the simulation method as shown inchapters4and5. Five types water cloud are examined in the research, the cleanwater cloud, the water cloud with rural type aerosol particles, the water cloud withcity type aerosol particles, the water clouds with aerosol particles from Harbin forsandstorms and the clear weather. The infrared transmission characteristics of watercloud have been calculated in3-5μm and8-12μm wavelength ranges.With the investigations in this dissertation, the simulation methods for solvingthe radiative heat transfer in participating media are developed. The thoroughresearches have been done for infrared radiative properties of aerosol particles andtheir influencing factors. The research resultes prepare the ground for opticalconstant inversion of aerosol particles. A equivalent optical constants inversionmodel has been proposed based on experimental measurement of the infrared transmittance of aerosol particles. The results can provide a reference for researchesin the field of radiative transfer, remote sensing, etc.