Dynamic effects of topography on dust particles in the Beijing region of China

Abstract

Dust particles are hazardous to human health and severely affect the city operations. However, there is few research on the topographic dynamic removal of near-surface dust particles. In this study, the surface meteorological and aerosol monitoring data if such an event was analysed. The event took place on March 27–29, 2018 in Beijing, China. Given the special topographic conditions in Beijing, various parameters, such as wind profile line data, four-dimensional variation Doppler radar data, and aerosol lidar data were used to determine the dynamic effects of easterly wind. The event could be divided into four stages. In Stage 1 (Dust aerosol transfer), the dust particles at higher elevation were transferred to upper atmosphere of Beijing through northern wind. These dust particles gradually moved to the lower atmosphere. The temperature inversion layer hindered the settlement of dust particles on the near-surface atmosphere. The dust particles could not penetrate the temperature inversion layer and moved to the near-surface layer. Anthropogenic aerosols of high concentrations were retained below the height of 1 km. In Stage 2 (development of dust particles), following the dynamics of easterly wind, the temperature inversion phenomenon gradually disappeared. The high-concentration dust particles in the higher atmosphere were transferred to the near-surface layer and settled down, thus mixing with the anthropogenic aerosol particles. In Stage 3 (decreasing dust aerosol concentration in the middle troposphere), the easterly wind clearly strengthened in the middle troposphere. Above this layer, the easterly wind weakened with height and formed uplifting airstreams, which coupled with the southerly airstream formed by the upper trough above Beijing. Furthermore, high-concentration aerosols were lifted to a certain height and could not spread to the upper atmosphere because of sinking airflow. In Stage 4 (removal of dust particles), the easterly wind reached the strength of low-level jet streams. The south-westerly wind was present above 2.5 km height. The high aerosol concentrations at the height of 2.0 km and below were lifted to the upper atmosphere and blown downstream by the strong south-westerly wind and the easterly wind coming from clean-ocean air masses, thereby concluding the dust particles’ event.