Influence of a boundary layer low-level jet on pollutant diffusion in Shouxian, Anhui Province in winter 2016
JING Cui-wen1, WANG Cheng-gang1, FENG Yan2,3
1. Key Laboratory for Aerosol-Cloud-Precipitation, China Meteorological Administration, Nanjing University of Information Science and Technology, Nanjing 210044, China; 2. Anhui Provincial Key Laboratory of Atmospheric Science and Satellite Remote Sensing, Anhui Institute of Meteorological Sciences, Hefei 230031, China; 3. Field Scientific Experiment Base of Ecological Meteorology for Typical Farmland in Huaihe River Basin, China Meteorological Administration, Shouxian National Climate Observatory, Shouxian 232200, China
Abstract：Based on the observation data and simulation data in Shouxian area of Anhui Province from December 16 to 17, 2016, the effect of a nocturnal boundary layer low-level jet on PM2.5 diffusion has been analyzed. In this process, the low-level jet has a wide distribution range and high intensity, the maximum wind speed can reach 10~12m/s, the wind direction difference between high and low layers can reach 90℃ during the development of the low-level jet. In the process of the low-level jet development, the jet axis is basically below 200m, and the minimum wind speed height of the low-level jet appears between 400~800m. The analysis shows that there are obvious differences in the impact of the low-level jet on pollutant diffusion at different heights. From ground to the low-level jet axis, PM2.5 overall decrease. The emergence of the low-level jet flow significantly enhances the turbulent mixing. Under the action of turbulence, the pollutants are mixed upward, making the layer PM2.5 significant reduction. The peak value of net mass flux can reach -103×10-3μg/(m2·s).The horizontal transportation of the low-level jet stream can bring cleaner air mass upwind, and also reduce PM2.5 concentration in this layer. However, compared with turbulence, its effect is small, and the net mass flux is only -2.9×10-3μg/(m2·s). When the low-level jet exists, the downward vertical wind speed will be strengthened. Under the action of vertical transportation, the pollutants in the upper layer will be transported downward, increasing the PM2.5 concentration in this layer, the net mass flux is about 11×10-3μg/(m2·s). Between the low-level jet axis and wind direction transition height, PM2.5 overall increase. This is because the turbulence transports high concentration pollutants in the low layer to this layer, making PM2.5 concentration increase. The net mass flux is about 23.9×10-3μg/(m2·s). Horizontal transportation makes this layer PM2.5 concentration increased slightly, and the net mass flux was about 2.3×10-3μg/(m2·s).The vertical transportation brings clean air mass at high altitude and reduces PM2.5 concentration, the net mass flux is about -6.6×10-3μg/(m2·s). Between wind direction transition height and LLJ minimum wind speed height, PM2.5 overall increase. Turbulence is still dominant, and the net mass flux is about 17.8×10-3μg/(m2·s).The vertical transport has a slight contribution, and the net mass flux is about 1.4×10-3μg/(m2·s). The horizontal transport plays a reducing role, and the net mass flux is about -3.7×10-3μg/(m2·s).
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JING Cui-wen, WANG Cheng-gang, FENG Yan. Influence of a boundary layer low-level jet on pollutant diffusion in Shouxian, Anhui Province in winter 2016. CHINA ENVIRONMENTAL SCIENCECE, 2022, 42(7): 3013-3022.
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