Three-dimensional structure of the atmospheric boundary layer and distribution of PM2.5 concentrations in the piedmont area of the North China Plain during a typical haze pollution process in winter (IMAGE)
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The Taihang Mountains have an adjusting effect on the meteorological conditions of the atmospheric boundary layer (ABL) in the North China Plain (NCP). For the thermal structure (figure b), the western part of the NCP near the mountains is significantly affected by drainage flow and subsidence warming, resulting in lower surface temperature, stronger elevated inversion layer, more stable atmospheric stratification, and worse conditions for vertical diffusion of pollutants. For the dynamic structure (figure c), the blocking effect of mountains causes frictional loss of kinetic energy and leads to airflow diversion. As a consequence, the calm wind layer in the western part of the NCP near the mountains is relatively thicker, which is not conducive to the horizontal transport of pollutants. Therefore, PM2.5 concentrations are higher in the western area (figure a).
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