Abstract: The two dust events affecting Beijing on 4-5, May, 2017 and 28-30, March, 2015 included both long range transport and dust backflow. The variation of meteorological elements, transmission trajectories, weather conditions and boundary layer characteristics of the two events were analyzed by using conventional meteorological observation data, atmospheric composition data, CALIPSO satellite monitoring and wind profile radar data. It was found that both events were caused by Mongolian cyclone. The dust aerosol transported through sand source during long range transport can be raised to a height above 700 hPa, and the main transport layer was located in the middle and lower troposphere. High-altitude jet stream intensity, inlet zone location and the structure of the secondary circulation showed important indications for the dust transport. The dust backflow was mainly affected by the low-level southerly wind belt, and boundary layer below 1 km was the main transport layer. The time lag of PM₁₀ concentration variation between Beijing and upstream cities was determined by whether the dust weather had been completely removed previously.

Key words: dust transportation, dust backflow, CALIPSO, wind profiler radar