Pollution Characteristics And Cause Analysis Of Fine Particulate Matter And O₃ In Shijiazhuang

Fine particulate matter(PM_2.5)and ozone（O₃）have complex chemical mechanisms,as well as the pollution sources and meteorological factors of PM_2.5 and O₃ are significantly correlated,therefore,the research on the causes of PM_2.5 and O₃ pollution has become the key to the continuous improvement of urban ambient air quality.In order to reveal the spatio-temporal characteristics,meteorological effects and pollution causes of PM_2.5 and O₃ pollution in Shijiazhuang,based on the ground-level six atmospheric pollutant(PM_2.5,O₃,PM₁₀,NO₂,CO and SO₂)from 46 state-controlled and provincial-controlled environmental monitoring stations in Shijiazhuang from December2018 to November 2019,and six atmospheric pollutant data from January 2019 to December 2022 in Shijiazhuang,as well as meteorological data（temperature,relative humidity,precipitation,wind speed,and wind direction）during the same period.The inverse distance weighted（IDW）and Pearson correlation coefficient has been applied to analyze the spatio-temporal distribution characteristics,correlation and meteorological relationships,clarified the key roles of PM_2.5 and O₃ in air pollution,and further explored the composite pollution characteristics and meteorological sensitivity of PM_2.5 and O₃.Based on the characteristics of PM_2.5 pollution,combined with carbon composition（OC and EC）and water-soluble inorganic ions（WSIIs）data from December 2019 to November2020,the PM_2.5 conversion rate was used for cause analysis research,and a backward trajectory model was used for spatial transmission source analysis.The heavy pollution of O₃（July to September）was selected to combine with the characteristics of VOCs components from July to September 2020,the ozone formation potential（OFP）and backward trajectory were analyzed to the causes of O₃ pollution.The research results were as follows:The annual average concentrations of six atmospheric pollutants in Shijiazhuang showed a downward trend during 2019 to 2022.The typical pollutant in autumn and winter was PM_2.5,showing a spatial pattern of high in the east and low in the west;O₃ was a typical pollutant in summer,with a spatial distribution state of high in the central and western regions and low in the peripheral regions.From the perspective of correlation,there was a significant positive correlation between PM_2.5 and humidity in autumn and winter,and a significant negative correlation with wind speed.There was a significant negative correlation among O₃,NO₂ and humidity in summer,a significant positive correlation with temperature and wind speed,and a weak positive correlation with PM_2.5.The component concentrations of PM_2.5 were WSIIs>OC>EC from December 2019to November 2020,especially those which were consistent with PM_2.5 in autumn and winter,and WSIIs contributing the most（68%）to PM_2.5 in Shijiazhuang.OC/EC>2,SOR>0.25 and NOR>0.1 indicated severe secondary pollution and stronger secondary transformation of SO₂ in Shijiazhuang.The pollution sources of OC and EC were similar,mainly from motor vehicle exhaust and coal combustion in spring,autumn and winter.In the transmission direction,the concentration of PM_2.5 in the transmission channel passing through Handan,Xingtai and southern district and county of Shijiazhuang was the highest.The VOCs changes showed a‘V’shaped trend from July to September 2020 in Shijiazhuang.Propylene,propionaldehyde,toluene,ethylene,and isoprene were the main dominant species.Biological sources of VOCs（BVOCs）,mobile sources,pharmaceutical and chemical sources,and solvent use sources had a significant impact.The daily variations of alkane,alkyne,aromatic hydrocarbon,OVOCs,alkyl halide,TVOC,and NO₂ exhibited a"U"shaped pattern of high nighttime and low daytime,while O₃exhibited an inverted"U"shaped pattern.O₃ pollution was related to close distance transmission and long-distance precursor transport,with Baoding,Langfang,Cangzhou,and Xingtai being important sources of pollution transmission.