Influence of Dynamic Process of Boundary Layer on Fine Particulate Matter Pollution Events in Chengdu
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Abstract:
In order to compare the similarities and differences of the two typical heavy pollution processes in Chengdu from December 2017 to January 2018, the generation and elimination are analyzed from the circulation situation, boundary layer transport and diffusion conditions by using the data of observation meteorological and wind profiler radar. The results show that: (1) Both processes were formed by stagnant weather. The zonal circulation prevailed in the upper layer, and the lower layer was an equal or weak pressure field with multiple layers of temperature inversion. The relative humidity was high at night, the wind speed was low, and the direction was changeable. Near the ground, the dominant wind direction was northwest, and west wind and wind direction affected the regional transport of air pollutants. (2) In the pollution accumulation stage, there was a small wind layer with an average wind speed of less than 2 m·s-1 and variable wind direction in the boundary layer. In the cleaning stage, this feature was not apparent. (3) The refractive index structure constant C2n and vertical velocity can be used as the criteria for vertical diffusion conditions. In the pollution accumulation stage, the height of the highvalue area of C2n was generally 500 to 1500 m, while it was above 3000 m in the removal stage. Meanwhile, the location and durations of the large value area of C2n and the large value area of vertical velocity were basically the same in the removal stage. (4) The recirculation index (RF) and the ventilation index (VI) were very indicative of the pollution process. In the pollution accumulation stage, the RF below 1000 m was less than 0.6, the nearsurface RF was less than 0.2, and the daily average VI was only 1455 m2·s-1. In the removal stage, the RF was above 0.7, and the VI exceeds 3000 m2·s-1. In addition, VI with a large value also played a role in transmitting upstream pollutants.
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Supported by:Beijing E-Tiller Technology Development Co., Ltd.
Supported by:Beijing E-Tiller Technology Development Co., Ltd.