Aerosol liquid water content (ALWC) plays fundamental roles in atmospheric radiation and chemical processes. However, there is little information about ALWC vertical distribution due to the lack of sufficient measurement. In this study, a novel method to retrieve ALWC using a polarization lidar is proposed. By analyzing lidar measurement combined with in situ chemical composition measurements at the surface, the particle linear depolarization ratio δp is found to be well correlated with the liquid water mass fraction. The method is built upon a valid relationship between δp and the ratio of ALWC to the particle backscatter coefficient. ALWC can be retrieved with a relative error of 30% with this method. A case study shows that the ALWC in upper levels of the boundary layer may be different from that at the ground, suggesting the importance of measuring ALWC vertical profiles during haze episodes. The study proves that polarization lidars have the potential to retrieve vertical distributions of ALWC which will benefit studies on haze formation.

The phase states of atmospheric aerosol particles affect their physical, chemical, and optical properties. Particles with different phase states exhibit different viscosities and various shapes that cause differences in their scattering polarization. In this study, a novel method for inferring the phase state of submicrometer particles using the particle linear depolarization ratio (δp) retrieved from polarization lidar is proposed. The values of δp during several haze episodes showed good correlation with the in situ-measured rebound fraction and ambient relative humidity. Two case studies verify that polarization lidar has the potential to infer the phase state profiles of submicrometer particles and that the particle phase state in the upper boundary layer may differ from that near the ground during haze episodes.

A new method to retrieve CCN number concentrations using multiwavelength Raman lidars is proposed. The method implements hygroscopic enhancements of backscatter and extinction with relative humidity to represent particle hygroscopicity. The retrieved CCN number concentrations are in good agreement with theoretical calculated values. Sensitivity tests indicate that retrieval error in CCN arises mostly from uncertainties in extinction coefficients and RH profiles.