Articles | Volume 16, issue 15
Atmos. Chem. Phys., 16, 9863–9873, 2016

Special issue: Anthropogenic dust and its climate impact

Atmos. Chem. Phys., 16, 9863–9873, 2016

Research article 05 Aug 2016

Research article | 05 Aug 2016

Polarization properties of aerosol particles over western Japan: classification, seasonal variation, and implications for air quality

Xiaole Pan1,2, Itsushi Uno2, Yukari Hara2, Kazuo Osada3, Shigekazu Yamamoto4, Zhe Wang2,1, Nobuo Sugimoto5, Hiroshi Kobayashi6, and Zifa Wang1 Xiaole Pan et al.
  • 1State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
  • 2Research Institute for Applied Mechanics, Kyushu University, Kasuga, Japan
  • 3Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
  • 4Fukuoka Institute of Health and Environmental Sciences, Daizaifu, Japan
  • 5National Institute for Environmental Studies, Ibaraki, Japan
  • 6University of Yamanashi, Yamanashi, Japan

Abstract. Ground-based observation of the polarization properties of aerosol particles using a polarization optical particle counter (POPC) was made from 27 October 2013, to 31 December 2015, at a suburban site in the Kyushu area of Japan. We found that the depolarization ratio (DR, the fraction of s-polarized signal in the total backward light scattering signal) of aerosol particles showed prominent seasonal variability, with peaks in spring (0.21–0.23) and winter (0.19–0.23), and a minimum value (0.09–0.14) in summer. The aerosol compositions in both fine mode (aerodynamic diameter of particle, Dp  <  2.5 µm) and coarse mode (2.5 µm  <  Dp  <  10 µm), and the size-dependent polarization characteristics were analyzed for long-range transport dust particles, sea salt, and anthropogenic pollution-dominant aerosols. The DR value increased with increasing particle size, and DR  =  0.1 was a reliable threshold value to identify the sphericity of supermicron (Dp  >  1 µm) particles. Occurrence of substandard air quality days in Kyushu was closely related with mixed type (coexistence of anthropogenic pollutants and dust particles in the atmosphere), especially in winter and spring, indicating that dust events in the Asian continent played a key role in the cross-boundary transport of continental pollution. Backward trajectory analysis demonstrated that air masses originating from the western Pacific contained large amounts of spherical particles due to the influence of sea salt, especially in summer; however, for air masses from the Asian continent, the dependence of number fraction of spherical particles on air relative humidity was insignificant, indicating the predominance of less-hygroscopic substances (e.g., mineral dust), although the mass concentrations of anthropogenic pollutants were elevated.

Short summary
Polarization properties of aerosol particles at a suburban site in the western Japan was studied on the basis of long-term observation and trajectory analysis. This study provides the detailed information on the polarization characteristics of particles from different origins, and proposed a reliable criterion to classify spherical and non-spherical particles. This study introduced a new method to investigate the mixed state of dust particle with anthropogenic pollutant.
Final-revised paper