Vertical distribution of optical and microphysical properties of smog aerosols measured by multi-wavelength polarization lidar in Xi'an, China

- A multi-wavelength and polarization lidar is established, and the algorithms for microphysical parameters of atmosphere aerosol, which do not need the prior lidar ratio, are proposed and provided.
- From the multi-wavelength lidar data, vertical microphysical properties such as volume size distribution, volume concentration, number concentration and effective radii in haze days, are retrieved using the inversion with regularization and analyzed.

In this study, a multi-wavelength polarization lidar was developed at the Lidar Center for Atmosphere Remote Sensing, in Xi'an, China to study the vertical distribution of the optical and microphysical properties of smog aerosols. To better understand smog, two events with different haze conditions observed in January 2015 were analyzed in detail. Using these data, we performed a vertical characterization of smog evolution using the lidar range-squared-corrected signal and the aerosol depolarization ratio. Using inversion with regularization, we retrieved the vertical distribution of aerosol microphysical properties, including volume size distribution, volume concentration, number concentration and effective radius. We also used the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model to analyze aerosol sources during the two episodes. Our results show that the most polluted area in the lower troposphere during smog episodes is located below a height of 1 km above the ground level; under more severe smog conditions, it can be below 0.5 km. In the case of severe smog, we found a large number of spherical and fine particles concentrated in the very low troposphere, even below 0.5 km. Surprisingly, a dust layer with a slight depolarization ratio was observed above the smog layer.