| The Sichuan Basin,one of the four major haze pollution areas in China,whose air pollution characteristics are different from the other three areas,affected by the unique topography.Meteorological conditions dominate the quality of the atmospheric environment in Sichuan Basin.Therefore,this article focuses on the meteorological point of view,and the Lagrangian dispersion model(HYSPLIT)is chose to carry out follow-up research.This research evaluated the application of in the Sichuan Basin.Combined with PM2.5 observation concentration data and Tsinghua University MEIC anthropogenic emission inventory,the high resolution of PM2.5emissions were estimated in the Sichuan Basin.The HYSPLIT model was used to obtain the PM2.5 transmission flux changes between urban clusters in different seasons in order to explore the mutual contribution of PM2.5 among urban agglomerations.The results of this thesis are summarized as follows:1)Large discrepancies in the resolution of meteorological data and in reaching height of the trajectory caused obvious deviation among the different backward trajectories obtained by the HYSPLIT model involving the horizontal,vertical and directional disparities.WRF output data and GDAS0p5 data could reproduce the ground high-frequency wind direction in the typical month of the four seasons.The wind speed of GDAS1 data had almost no correlation with the observed wind speed in October.Affected by the complex terrain of the Sichuan Basin,more details of atmospheric movement could be captured by the trajectory obtained from the WRF output data.The GDSA1 data to drive HYSPLIT distorted the description of the wind field in the plateau area,resulting in part of the trajectories arrived at Chengdu came from the plateau area.It is recommended that high-resolution meteorological data that can identify the topography of the basin should be selected when the HYSPLIT is applicated in the Sichuan Basin,and the simulated height in the four seasons should set to be 300 meters.2)Combined with the daily average concentration of PM2.5 at the observation sites and the HYSPLIT model,a transmission coefficient matrix connecting the emission source point and the observation receiving point was constructed.To solve the cost function representing the difference between the predicted PM2.5 concentration by the model and the observed PM2.5concentration,the Tsinghua University MEIC anthropogenic source emission inventory as the priori emission information of PM2.5 in the Sichuan Basin was added to the process,and the source strength corresponding to the minimum cost function was considered to be the required emission source.The estimated daily PM2.5 emission sources in January 2018,had relatively slight daily changes which showing a scattered distribution with the high-value center located at the Basin urban area,and the emission intensity of Chengdu and Chongqing urban centers was significantly higher than other urban areas.Compared with the MEIC inventory in January2016,the PM2.5 emissions of Chengdu and Chongqing had dropped significantly.3)There were evident seasonal changes in the diffusion capacity of PM2.5 at different heights.The near-surface layer PM2.5 contributed a lot to the surrounding urban agglomerations.The PM2.5 transmission flux between urban agglomerations at the middle and upper tropospheric had increased significantly,and it could be radiated a wider range.Within the entire boundary layer,the PM2.5 were mutually affected by the Chengdu Plain,the southern and the northeastern urban agglomeration in Sichuan Basin.The six urban agglomerations in Chongqing were mainly exported from the main urban area of Chongqing.The transportation from the northeast and east of Chongqing to the northeast of Sichuan was also obvious.In January and October,the contribution characteristics between the urban agglomerations were similar.The southern region in Sichuan and Chengdu plain urban agglomerations were the main receiving areas and were affected by PM2.5 transmission in most parts of the basin.In April,the PM2.5 in various urban agglomerations could radiate farther from the main urban area of Chongqing.In July,the PM2.5 in the northeast of Sichuan Province received an increase in PM2.5 transmitted from the southeast direction.In addition,in April and July,the PM2.5 transmission flux of each layer was significantly lower than that in January and October.As the intensity of the emission source decreased,the mutual influence between the urban agglomerations also dropped.In the joint prevention and control of air pollution areas,it is extremely important to update the emission sources in time. |
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