| Xi’an has an important strategic position in the National Belt and Road Initiative,and it is also the ninth national central city in China.Xi’an’s atmospheric environmental quality has always been an important factor affecting the city’s image.This study is based on the monitoring data of the National Air Quality Control Substation of Xi’an from March 2018 to February 2019,revealing the characteristics of air pollution in Xi’an.The emission inventory method and the backward trajectory model are used to specifically analyze the source of atmospheric particulate matter,and to identify the key sources of atmospheric particulate matter from the perspectives of local source emissions and external source area transmission.The main conclusions are:（1）The average annual concentrations of six air pollutants in Xi’an in 2019 are102ug/m3 for PM10,58ug/m3 for PM2.5,9ug/m3 for SO2,48ug/m3 for NO2,0.9mg/m3 for CO and 89ug/m3 for O3.The main pollutants have obvious changes with the month.The main pollutants in the heating season from January to March and November to December are mainly PM2.5,and the main pollutants from April to May are mainly PM10.From June to August,the main pollutant in the hot season is mainly ozone.And the main pollutant in September-October is mainly NO2.The maximum value of AQI in Xi’an appears at 1 am,gradually decreases from 1 am to 8 am,rises slightly from 8 am,and it continues to decline from 13:00 to 18:00.The AQI value is the smallest at 18:00,and it continues to rise after 18:00 high.During the study period,PM10 and PM2.5. have a high correlation,the emission sources are similar,and the migration and transformation laws in the atmospheric environment are similar.Affected by seasonal changes,the correlation coefficient r between the mass concentration of PM10 and PM2.5. is 0.66 in spring,0.83 in summer,0.93 in autumn and 0.94 in winter.（2）The emission of PM10 in Xi’an was 27151.33 tons in 2018.Organized emission from industrial sources is the most important contribution source of PM10,with a contribution rate of 42.41%.The contribution rate of building construction and road mobile sources is also large,respectively 25.68and%23.49%.In 2018,the emission of PM2.5. in Xi’an was 14767.90 tons.The largest source of PM2.5. is also organized emissions during industrial production,accounting for 50.67%.Road mobile sources are the second largest source of PM2.5,accounting for 30.50%.（3）Through analysis and calculation of the potential contribution sources of PM2.5. in Xi’an,it is concluded that the regions contributing to the PM2.5. concentration in Xi’an are mainly concentrated in the central Gansu along the Hexi Corridor in spring,mainly concentrated in the eastern region in summer and mainly concentrated in Baoji region in autumn.In winter the regions contributing to the PM2.5concentration in Xi’an are mainly concentrated in Guanzhong area around Xi’an,Yuncheng area in southern Shanxi province,and Zhengzhou,Luoyang and Sanmenxia areas in Henan province. |
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