Study on the influence of different aerosol mixing states on lidar ratio

             After years of development, Mie lidar has become an important technical means to explore aerosol particles in the atmosphere, and has been widely used to explore the optical and physical properties of aerosols in atmosphere. By Using backscatter signal collecting by lidar, optical characteristics of aerosols can be qualitatively analyzed. However, in order to get the actual value of optical parameters, the accurate lidar ratio (LR) (the ratio of extinction coefficient to back-scattering coefficient) is needed in inversion.

            Using the Mie scattering theory, the key parameter of inversion: LR, can be measured out. The value of LR has been discussed in detail by changing complex refractive index, size parameter  and field angle of a single particle. It is found that when the scale parameter is greater than 0.6, the value of LR increases first and then decreases with the increasing scale parameter, and there are several extremums; the value of LR decreases with the increasing imaginary part of the complex refractive index; the value of LR increases with the increasing filed angle.

            To study the influence of different mixing states on optical parameters of aerosol clusters, a three-component optical equilibrium spherical aerosol model is assumed. The results shows that when the mixing states of aerosol are complete external mixture, complete uniform internal mixture and complete coated mixture, the value of LR appears to be: complete uniform internal mixture > complete external mixture > complete coated mixture.

            Assuming that the hygroscopic growth factor of aerosol is a constant which does not increase with the particle size and its value is GF = 1.5[p2] , the value of LR after hygroscopic growing is discussed. It is found that the value of LR will increase after hygroscopic growing, but it still follows the law that: complete uniform internal mixture > complete external mixture > complete coated mixture.

            By correcting the value of LR, accurate extinction coefficient and back-scattering coefficient can be measured out with inversion. The production of lidar will be quantified instead of qualitative after doing this.