Investigation of aerosol absorption with dual-polarization lidar observations

Polarization lidar has been widely used in recent decades to observe the vertical structures of aerosols and clouds in the atmosphere. To obtain more information from polarization lidar measurements, we developed a dual-polarization lidar system that can detect polarization measurements simultaneously at both 355 nm and 532 nm. The vertical distributions of atmospheric aerosols and clouds over northern China were successfully observed by the developed lidar. Observational data during two typical cases (dust events and haze episodes) were used for the analysis in this study. The results showed that for dust-dominated aerosols, the depolarization ratio (DR) at 532 nm was larger than that at 355 nm, but that for air pollutants was smaller. Our results also show that dual-polarization measurements can be used to largely improve aerosol classification. Moreover, we found that there is a good relationship between the absorption coefficient of aerosols and the ratio of DRs at 532 nm and 355 nm for dust aerosols. These results confirm that the absorption characteristics of dust aerosols cause a difference in DR at the UV and VIS wavelengths, and implying that aerosol absorption may be determined by polarization lidar at the ultraviolet and visible wavelengths.