Study on variations in lidar ratios for Shanghai based on Ramanlidar

Abstract. Accurate Lidar ratios (LR) and better understanding of their variation characteristics can not only improve the retrieval accuracy of parameters from elastic lidar, but also play an important role in assessing the impacts of aerosols on the climate. Using the observational data of Raman lidar in Shanghai from 2017 to 2019, the LR at 355 nm were retrieved and their variations and influencing factors were analyzed. Within the height range of 0.5 km–5 km, about 90 % of the LR were distributed in 10 sr–80 sr with an average value of 41.0 ± 22.5 sr, and the LR decreased with the increase of height. The volume depolarization ratios (δ) were positively correlated with LR, and they also decreased with the increase of height, indicating that the vertical distribution of particle shape was one of the influencing factors of the variations of LR with height. LR had a strong dependence on the original source of the air masses. Affected by the aerosol transported from northwest of Shanghai, the average LR was the largest, 44.2 ± 24.7 sr, accompanied by the most irregular particle shape. The vertical distributions of LR were affected by the atmospheric turbidity, with the greater gradient of LR under the clean conditions. The LR above 1 km could be more than 80 sr, when Shanghai was affected by the biomass burning aerosols.