Abstract: In this paper, the global NCEP reanalysis data, hourly pollutant concentration data, wind profiler radar and ground routine observation data in Beijing were used to analyze a haze-dust pollution process from March 26 to March 29, 2018. The results showed that the PM_2.5 peak concentration was 242 μg·m^-3, and PM_2.5/PM₁₀ ratio was 0.86 during haze period. Affected by Mongolian cyclone, the concentration of PM₁₀ increased explosively, and the growth rate reached 912 μg·m^-3·h^-1, and the proportion of PM_2.5/PM₁₀ decreased to 0.11. By analyzing of the horizontal wind field, ventilation index and vertical velocity in the boundary layer, it could be seen that the southwest wind dominated the boundary layer during haze period, and the average ventilation index was 15 907 m²·s^-1. The steady weak upward or subsidence movement was dominant. In the period of sand, the average ventilation index was 9 226 m²·s^-1. Vertical velocity was earlier than variation of pollutant concentration in advance. Based on the backward trajectory model and potential source contribution analysis method (PSCF) results, central and southern Hebei province and central Shanxi province contributed significantly to PM_2.5 in Beijing during the haze period. While in the sand period, the PM₁₀ concentration in Beijing was mainly from the central of Inner Mongolia and western of Liaoning province.

Key words: haze, sand dust, wind profiler radar, ventilation index