Abstract: In March 2021, there were three large-scale sand-dust pollutions in northern China. In order to accurately understand the transmission process of these three sand-dust pollutions, the vertical detection results of the Mie scattering aerosol lidars distributed in the Beijing-Tianjin-Hebei region in this period were analyzed and studied. The vertical detection results show that the transmission sequences of the three sand-dust pollutions processes in March 2021 were almost the same: Zhangjiakou, Beijing, Langfang (Baoding), Tianjin, Qinhuangdao, sequentially. During this period, the pollution weather in the Beijing- Tianjin-Hebei region was affected by northwest and north winds, resulting in sand-dust pollutions in this region. Among them, Zhangjiakou and Beijing in this area were seriously affected by the three pollution events. During the two more serious sand-dust pollutions from March 14 to 18 and from March 27 to 31, pollution was transmitted from northwest to southeast in Beijing, Langfang and Tianjin, and the concentration of pollutants in the three cities decreased in turn. Overall, during the three sand-dust pollutions in March 2021, the impact on various cities gradually weakened as they transported from northwest to southeast. Based on the air mass movement trajectory and the retrieve mapping, a scientific analysis was made on the pollution processes of the three sand-dust events in the Beijing-Tianjin-Hebei region, which provides a case and reference for the prevention and control of sand-dust pollution in the future.

Key words: sand-dust transport, Mie scattering lidar, extinction coefficient, depolarization ratio