Light Absorption Properties Of Dust Aerosol And Effective Refractive Index Study

Dust aerosol plays an important role in affecting the regional and global climate,but the radiation forcing still suffers from great uncertainties,which partially stem from the dust absorption uncertainty existing in both the short and long wave spectral range.Improving the knowledge of dust refractive index and its relation to mineral composition is crucial for understanding the effects of dust on atmospheric radiative transport simulations and reducing uncertainty in climate models.In addition,non-spherical and inhomogeneous characteristics of dust are important factors that are fundamential to remote sensing and climate simulations.An optimized dust model incorporating the aforementioned factors is required for computing dust optical properties.Major works and conclusions of this paper are summarized as follows:1.An inhomogeneous dust model was developed to obtain the dust effective refractive index by using the complex refractive index of each mineral component from the literature.The optical properties of inhomogeneous particles were first calculated by T-matrix method,and then the effective refractive index of dust was retrieved by comparing the optical properties of inhomogeneous particles with their couterparts computed from homogeneous spherical particles.In the short wave(0.2-1.0?m),we found that hematite dominates the absorption characteristics of dust.We speculated that the available complex refractive index of hematite in the literature may be overestimated.The effective refractive index at long wavelengths(6.0-14.0?m)from the present study is in good agreement with the measured values in the literature.2.The super-spheroid model was first shown to be successfully simulate the measured phase matrix in Granada-Amsterdam database.The Lidar backscattering observations were further simulated by using nonspherical and inhomogeneous particle models.We found that,compared with the homogeneous model,the inhomogeneous super-spheroid model can better simulate the lidar ratio observations at 0.355?m.In addition,the differences of the depolarization ratio and the lidar ratio in the near-backscattering direction(174~°,176~°,178~°)and exact backscattering direction(180~°)of the dust particles were analyzed quantitatively.The results showed that the difference of the lidar ratio can not be ignored.3.The absorption properties of dust in the thermal infrared bands were studied by using Cr IS(Cross-Track Infrared Sounder)infrared hyperspectral brightness temperature spectrum combined with theoretical simulations based on the RTTOV(Radiative Transfer for TOVS)model.We found that the peaks of brightness temperature differences are associated with specific mineral composition.By using these peaks,dust composition(e.g.,quartz,kanoite and calcite)can be indentified from the Cr IS satellite observations the regional differences of kaolinite were found.