Vertical Distribution and Transport of Aerosols during a Dust Event in Xinjiang,Northwest China

Dust aerosols profoundly influence the radiative balance of the earth–atmosphere system and hence the global and regional climates.In this study,using multi-source satellite and ground-level observations combined with meteorological data,we investigated the three-dimensional evolution and transport characteristics of aerosols during a dust event that occurred in Xinjiang,China from 19 to 21 March 2019.Analysis of the meteorological data reveals that the dust air mass initially appeared in the northwest of Xinjiang and was subsequently transported to the Hami and Turpan areas due to the prevailing northwesterly winds,after which the direction of the airflow shifted due to topography,and the dust air masses were transported into southern Xinjiang.The air quality in the affected areas decreased rapidly,accompanied by a significant increase in aerosol optical depth (AOD),with the maximum value exceeding 3.5 in some areas.In addition,the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations(CALIPSO) data reveal that the aerosol particles in the dust-affected areas were mainly dust aerosols,with small amounts of pollutant dust aerosols.A reduction in the attenuated backscatter coefficient (β532||) was found with increasing altitude,with the dust aerosol pollution mainly distributed in the lower troposphere.The size of dust particles in the lower troposphere was relatively small and irregular.The depolarization ratio (PDR) values at altitudes of 8–10 km were relatively lower than those recorded in the lower troposphere,whereas the color ratio (CR)values were higher,which may have been influenced by the sparse vegetation coverage and poor subsurface conditions in Xinjiang,and attributable to the fact that regular large particles of dust are more likely to be dispersed to altitudes between 8 and 10 km within a short period of time.As a consequence of the meteorological conditions and topography,the dusting process in Xinjiang persisted for a relatively long period.These findings will contribute to enhanced understanding of the vertical distribution of aerosols in Northwest China.