Spatial And Temporal Evolution And Transport Characteristics Of Atmospheric Pollutants In The Sichuan Basin

With the rapid development of society and economy,people became to pay more attention to air pollution.The Sichuan Basin is one of the four regions with serious air pollution in China.It is necessary to systematically analyze the temporal and spatial distribution and variation of pollutants,transportation characteristics and the causes of heavy air pollution.Firstly,the hourly air pollutants data(CO,NO₂,O₃,PM_2.5,PM₁₀,SO₂)of 17 cities in the Sichuan basin provided by the national environmental monitoring station from 2015 to 2018 are used to define the chief pollutants in the Sichuan Basin(O₃,PM_2.5,PM₁₀)and discuss their temporal and spatial distribution and variation characteristics.Secondly,GDAS data and HYSPLIT(The Hybrid Single-Particle Lagrangian Integrated Trajectory Model)backward trajectory model combined are used to systematically analyze the transport pathways and potential source areas in the whole year and the four seasons of 2018,and further analyze the external transport pathways of chief pollutants in Chengdu.Finally,based on the hourly air pollutants data of national environmental monitoring station,5 continuous heavy pollution events of the Sichuan Basin from 2015 to 2018 were selected.An event in January 2017 were selected to discuss its variation characteristics and analyze the formation and dissipation process of this event by data analysis and numeric stimulation.The main conclusions are as follows:(1)Zigong,Chengdu and Deyang are the three cities with the most serious air pollution in the Sichuan basin.The air pollution degree of the cities inside the basin is higher than that at the edge of the basin.The chief pollutants in the Sichuan Basin are PM_2.5,PM₁₀,and O₃.All three pollutants are significantly present in spring and autumn.O₃is mainly in summer and PM_2.5and PM₁₀are mainly in winter.In terms of temporal variation,the concentration of O₃ increased from 2015 to 2018,but the concentration of PM_2.5and PM₁₀decreased.The concentration of O₃is the highest from May to August,and the lowest from December to January of the next year.The variation of PM_2.5and PM₁₀is opposite to that of O₃.The diurnal variations of O₃in unimodal pattern,and the diurnal variations of PM_2.5and PM₁₀are in bimodal pattern.In terms of spatial distribution,the annual mean value of O₃is high in the middle and low in both sides of the basin,but PM_2.5and PM₁₀are high in Zigong and Chengdu.In terms of seasonal spatial distribution,O₃high value area is located in the middle of the basin in spring and summer and in Ya'an and the west of the basin in autumn and winter.The spatial distribution of PM_2.5and PM₁₀in four seasons are basically consistent with the annual spatial distribution.(2)The transport pathways and potential source area in whole year and different seasons have been analyzed in this study,the trajectory in the Sichuan Basin is mainly short-distance inside the basin in the whole year and the four seasons of 2018.The exogenous three chief pollutants in the basin are mainly transported within the basin,but there are also seasonal differences.The potential source area of O₃is mainly located in Luzhou.The potential source areas of PM_2.5are mainly distributed in Ziyang,Neijiang,Zigong and western Chongqing.The potential source areas of PM₁₀are mainly distributed in Zigong and western Chongqing. For the outward transport pathways of pollutants in Chengdu,the trajectory in Chengdu mainly spreads to Deyang and Mianyang.In spring,Chengdu mainly transports particles to Deyang,Mianyang and Nanchong.In summer,the southern part of A'ba and the southern part of Shaanxi Province are easily polluted by O₃ of Chengdu.In autumn,Ya'an is more likely to be affected by pollutants in Chengdu.In winter,Ziyang and Neijiang are more likely be impacted by PM_2.5 and PM₁₀of Chengdu,and Ya'an and outside province in the northeast of Sichuan province are also be affected.(3)In 2015-2018,there were 5 continuous heavy pollution events in the Sichuan Basin,and Chengdu are the most polluted cities.During the heavy pollution events from January 1 to 6,2017,the AQI variation in Chengdu,Zigong and Dazhou were relatively consistent,reaching a peak near 03:00 on January 5. Meteorological data and WRF simulation results show that warm southwest air flow in 700h Pa,continuous temperature inversion layer,small surface wind speed and vertical speed and the convergence area of wind make pollutants accumulate rapidly,forming this continuous heavy pollution event.The pollutants in Chengdu caused by this continuous heavy pollution event are mainly transported within the basin,from the west of Chengdu,the west of Meishan and the southeast of Mianyang to convergence area in eastern Chengdu.The potential source is mainly located in Chengdu,Mianyang,Deyang and Meishan in Sichuan Basin.