Spatial And Temporal Characteristics,Sources And Environmental Impact Of Ambient VOCs In Zhengzhou

In recent years,Zhengzhou has faced a complex air pollution problem of Ozone(O3)and PM2.5.Volatile Organic Compounds(VOCs)have attracted widespread attention as the key precursors for the formation of O3 and Secondary Organic Aerosol(SOA).In this study,four sites in Zhengzhou were selected for off-line sampling of VOCs from July 2020 to June 2021.We analyze the characteristics of concentration,species,spatial and temporal distribution,sources of VOCs and their difference,and assess the contribution of VOCs to the formation of O3 and SOA and their toxic effects.The Ozone Formation Potential(OFP),Secondary Organic Aerosol Potential(SOAP)and toxicity data of each VOCs species were also combined to assess the comprehensive impact of VOCs on the environment.First,based on laboratory analysis,the average mixing ratio of VOCs in Zhengzhou during the observation period was 36.85×10-9 and the proportion of alkanes was the highest(33.4%).Acetone,ethyl acetate and ethane were abundant species.The seasonal variation was winter(43.98×10-9)>autumn(37.09×10-9)>summer(35.27×10-9)>spring(31.13×10-9).The spatial variation was Zhengzhou University(47.20×10-9)>Zhengzhou City Monitoring Station(37.36×10-9)>Jingkai District Management Committee(34.20×10-9)>Gangli Reservoir(28.90×10-9).Correlation analysis showed that the average mixing ratio of VOCs was closely related to meteorological factors.During a typical O3 pollution period in summer,the average mixing ratio of VOCs was 40.72 ×10-9.The average mixing ratio of VOCs decreased by 8.3%on O3 pollution days compared with non-pollution days,and the components of VOCs showed a decreasing trend on O3 pollution days.The daily variation of VOCs showed a characteristic of higher nighttime than daytime,with the morning peak occurring between 6:00 and 9:00.Then,based on the ratio of specific compounds and PMF model,the main sources of VOCs in Zhengzhou are vehicle emission(29.1%),solvent usage(25.8%),industrial emission(22.2%),fuel evaporation(18.9%)and biogenic source(4.1%).Solvent usage(31.9%)and vehicle emission(24.4%)contributed more in summer;vehicle emission(43.8%)and solvent usage(21.4%)contributed more in autumn;industrial emission(31.2%)and vehicle emission(31.0%)contributed more in winter;and in spring it was solvent usage(34.9%)and industrial emission(22.9%)that contributed more.Vehicle emission,solvent usage and industrial emission were all important emission sources at each sampling site,with the total contribution more than 73.5%.The value was up to 93.4%at Jingkai District Management Committee site.The contribution of fuel evaporation at Zhengzhou University site is outstanding,at 24.2%.Finally,the contribution of VOCs to O3 and SOA formation and their toxic effects show that alkenes and aromatics contributed more to OFP,with alkenes contributing most in summer and autumn,and aromatics contributing most in winter and spring.Aromatics contributing most in Jingkai District Management Committee site,and alkenes contributing most in other sites.Aromatics were the component contributing most to SOA formation in different seasons and sampling sites,while the toxic effects of halocarbons and aromatics were higher.The results of the comprehensive environmental effects showed that aromatics were the components that contributed the most,and toluene,benzene and methylene chloride were the species that contributed more.