Analysis Of Spatiotemporal Variation Characteristics And Causes Of Air Pollution In Urban Areas Of Zunyi Cit

In this thesis,the spatial and temporal distribution characteristics and change trends of major air pollutants were systematically studied through the air quality automatic monitoring data of five air state control points in the central city of Zunyi from 2010 to 2019,along with correlation analysis,backward trajectory clustering analysis and potential source analysis,and combined with the major air pollution emission reduction measures taken in Zunyi in the past ten years to evaluate the effect of emission reduction measures on air quality improvement,the main findings obtained are as follows.（1）From 2010-2019,the ratio of six parameters of good days in urban areas of Zunyi City increased significantly,SO₂,PM₁₀,PM_2.5quality concentration decreased significantly in ten years,NO₂,O₃,CO did not change much,and O₃had an upward trend in the past two years;The peak of O₃pollution in Zunyi is in August,while the highest concentration of other 5 pollutants such as SO₂usually appeared between December and February of the following year;O₃hourly concentration changes show an obvious single-peak change,with the peak occurring at 13:00-16:00,while the hourly concentration changes of the remaining five pollutants show an obvious double-peak and double-valley trend,with the time of rapid increase in concentration coinciding with the peak commuting period;In recent years,the number of days with PM₁₀and PM_2.5as the primary pollutants has decreased significantly,while the number of days with O₃as the primary pollutant has increased year by year.Atmospheric pollution has gradually changed from particulate pollution to photochemical pollution type;on the spatial scale,the highest annual average concentrations of PM_2.5,CO and NO₂all appear at the Dingzikou site,the highest annual average concentrations of PM₁₀and SO₂appear at the Zhoushuiqiao site,and the highest annual average concentration of O₃appears at the Fenghuang Mountain site.（2）The hourly mean values of O₃and NO₂were significantly negatively correlated with a correlation coefficient of-0.440;Each pollutant was significantly correlated with wind speed,air temperature,atmospheric pressure,and relative humidity（P<0.01）,among which the correlation with O₃was the most obvious,with correlation coefficients of 0.195,0369,-0.222,and-0.663 with wind speed,air temperature,atmospheric pressure and relative humidity.（3）The results of backward trajectory clustering analysis show that Zunyi City is mainly influenced by air masses in the northeast,southeast and due west directions,and its potential source areas are mainly distributed in the surrounding Bijie area,Liupanshui City and Xinyi City in southwest China’s Qianjiang Province,as well as in Zhangao City and Wenshan County in Yunnan Province.（4）Among the air pollution control measures,SO₂and particulate matter control measures are the most effective.Through the elimination of coal-fired boilers and strict control of the circulation of low-quality coal in urban areas,the treatment of soot-type pollution during the 12th Five-Year Plan achieved phased results,and the annual average concentrations of SO₂and particulate matter both dropped rapidly after 2014;During the"Thirteenth Five-Year Plan"period,the concentration of particulate matter has been continuously reduced through special treatment of dust,and the polluted weather has been reduced from 90 days in 2014 to 7 days in 2019,and no more heavy polluted weather has occurred since 2017,and the annual average values of major pollutants have all met the requirements of the secondary standard limits of the Ambient Air Quality Standards in 2018.The primary pollutant for the whole year has changed from PM_2.5to O₃.