| dc.description | Atmospheric particles, such as aerosols, have a wide range of sizes, shapes, and compositions. It is difficult to determine the single scattering properties of an aerosol taking account of all its possible physical properties. A numerical method, known as the finite difference time domain (FDTD) method, can be used for this purpose. However, because aerosol compositions are complicated, the effective medium approximation (EMA) is usually employed. In this thesis, various EMAs are discussed and numerically tested using the FDTD method. A composite particle modeled by a spherical particle with multiple spherical inclusions is used to test the EMAs. It is found that the applicability of the EMAs depends on the physical properties, the spatial arrangement, and the number of the inclusions inside the host sphere. It is found that the Bruggeman and the quasi-crystalline approximation with coherent potential and Percus-Yevick (PY) pair distribution (QCA-CP-PY) mixing rules show better accuracy than other analytical EMAs for an inclusion size much smaller than the wavelength and for a volume fraction less than 10%. For a larger inclusion, the extended Bruggeman method and the QCA-CP-PY give more accurate results. When only one inclusion is inside the host sphere, the extended Maxwell-Garnett is more accurate. Effective refractive indices obtained from the Bruggeman mixing rule show a good agreement with the FDTD results for very small inclusions. For a larger inclusion, a combination of Bruggeman and the Maxwell-Garnett mixing rules shows a good agreement. | en_US |
