Optical properties of mixed aerosol layers over Japan derived with multi-wavelength Mie–Raman lidar system

Abstract

Mixing state of aerosols and optical properties including lidar ratio, particle depolarization ratio, and Ångström exponent were investigated at Fukuoka in western Japan using a multi-wavelength Mie–Raman lidar (MMRL), various aerosol mass-concentration measurements, and a polarization optical particle counter during Winter–Spring 2015. Aerosol extinction coefficient, backscatter coefficient, and depolarization at 355 and 532nm and attenuated backscatter coefficient at 1064nm are obtained from the MMRL measurements. Ten aerosol episodes were classified into three categories (air pollution, mineral dust, and marine aerosol) based on aerosol mass-concentration measurements in the fine-mode (particle diameter Dp<2.5μm) and coarse-mode (2.5μm<Dp<10μm). The mean lidar ratio for air pollution was 57±4sr at 355nm and 53±8sr at 532nm with Ångström exponent of 1.4±0.5. For mineral dust, a slightly high averaged lidar ratio (50±7sr at 355nm and 54±9sr at 532nm) was obtained with relatively high Ångström exponent of 0.8±0.3 owing to contributions from fine-mode particles (PMf). The mean particle depolarization ratios of 13±8% at 355nm and 16±6% at 532nm also suggest mixing of mineral dust and anthropogenic fine-mode aerosols. The lowest lidar ratio was obtained for marine case. Classification of aerosol types using the lidar ratio and particle depolarization ratio was conducted based on the results obtained in this study. The classified aerosol types almost corresponded to aerosol category obtained by previous studies. We found no remarkable correlation between the fraction of black carbon and the lidar ratio: this might be due to the complexity of the mixing state among various aerosols. The obtained lidar ratio was rather correlated with the ratio of PMf to PM10, representing the mixing state of fine- and coarse-mode particles.