Abstract
Abstract. The light scattering characteristics of sulfate, one of the main pollutant particles in haze, are calculated by T-Matrix method at a target wavelength of 550 nm. The variation between shape factors (such as effective radius and aspect ratio) and scattering phase functions with different types and shapes are analysed in small scale range. The influence of shape factors on scattering cross section and depolarization ratio of particles are also discussed. Results show that the shape of particles has great effects on the spatial distribution of scattering energy, and the scattering properties of particles are sensitive to aspect ratio. The depolarization of spherical particles is close to zero, while the difference between ellipsoidal and cylindrical particles reaches several orders of magnitude. When the equivalent radius is larger than 1.0 μm, the mean depolarization ratio of the non-spherical particles is greater than 0.2. The mean depolarization ratio and scattering cross section of non-spherical particle change continuously with a certain aspect ratio and particle size range, and the shape of some particles can be therefore distinguished under certain conditions.
Highlights
The haze phenomenon is caused by the accumulation of primary pollutants in the atmosphere and secondary pollutants formed by chemical reactions under certain atmospheric capacity (He at al. 2013; Wu, 2012). Chow et al (2002) found that the contribution of fine particles (D2.5μm) is about 30%
Because the depolarization of cylindrical particles with different shapes fluctuates slightly with the change of aspect ratio, it is more difficult to distinguish the specific shape of cylindrical particles by depolarization than that of ellipsoidal particles
The scattering characteristics and aspect ratio of sulfate particles in haze are closely related to the equivalent radius of particle
Summary
The haze phenomenon is caused by the accumulation of primary pollutants in the atmosphere and secondary pollutants formed by chemical reactions under certain atmospheric capacity (He at al. 2013; Wu, 2012). Chow et al (2002) found that the contribution of fine particles (D2.5μm) is about 30%. The typical factor leading to haze event is the concentration of fine particles, especially the concentration of sulfate and nitrate, as well as the relative humidity of the atmosphere. Researches mainly focus on the subjects of the physical and chemical components, optical properties and causes of haze by means of ground-based observation, meteorological analysis, aerosol particle transformation, remote sensing inversion and model simulation. A polarized optical particle counter (POPC) has been developed by both the Beijing Institute of Atmospheric Physics and Chinese Academy of Sciences to measure the morphological characteristics of aerosols. It can distinguish aerosol types by polarization information of scattered light (Tian et al 2018). The changes of forward and backward scattering, scattering cross section and depolarization with aspect ratio and equivalent radius, and that of scattering phase function with scattering angle are analyzed
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