| Promoted by“Rise of Central China”strategy,Wuhan has been developing rapidly,which has resulted in serious ozone（O3）pollution.Tropospheric O3 has a significant impact on human health,plant growth and atmospheric oxidation due to its high oxidation.The formation process of O3 is complicated,and there is not a linear relationship between O3 and its precursors.Thus,by analyzing the O3 characteristics and O3 photochemical mechanism,deepening the understanding of O3 formation process and identifying the important pollutants can help to develop accurate and effective O3 reduction measures.112 volatile organic compounds（VOCs）samples were collected simultaneously at an urban site（Ziyang,ZY）and a suburban site（Huangpi,HP）in August 2018 in Wuhan.The samples were analyzed by gas chromatograph-mass spectrometer/flame ionization detector（GC-MS/FID）,and the photochemical reaction processes during the sampling period were simulated by a zero dimensional photochemical box model（PBM-MCM）.The characteristics of O3 and its precursor,the relationship between the O3 and its precursor and O3 photochemical formation mechanism in Wuhan in summer were analyzed in this study.The main conclusions are as follows:（1）At ZY,the O3 average mixing ratios in August was 36.5±1.6 ppbv while the the O3 average mixing ratios at HP was 47.1±1.5 ppbv,but the levels of O3precursors（NO,NO2,CO and VOCs）at ZY were higher than those measured at HP.During the sampling period,the concentrations of O3,NO,NO2 and CO on O3 episode days at ZY and HP were significantly higher than those on non-O3 episode days.The higher temperature,lower relative humidity,and lower wind speed on O3 episode days might be helpful for the formation and accumulation of O3 and its precursors at both sites.（2）Alkanes accounted for the highest proportion at ZY and HP,but there were differences in the proportion of each component between ZY and HP which might indicates the difference of VOCs sources between ZY and HP.The benzene/toluene ratios of two sites indicate that the level of VOCs was more affected by the motor vehicle at ZY,while the level of VOCs at HP was more affected by the coal burning.（3）O3 formation was AVOCs-limited at ZY on O3 episode days and non-O3episode days,while it was generally cooperatively controlled by AVOCs and NO at HP on O3 episode days and non-O3 episode days.According to the comprehensive evaluation of the concentration,RIR value and OH reactivity of NMHCs,the results suggest that acetylene and i-pentane had a greater impact on O3 pollution at ZY,while propane,propylene and i-pentane play important roles in O3 pollution at HP.（4）The simulated concentrations and the formation or loss rates of OH and HO2on O3 episode days were much higher than those on non-O3 episode days at ZY and HP,implying more efficient radical cycling on O3 episode days at both sites.At two sites,the reaction of HO2+NO was the most predominant pathway of the OH production,and OH+VOCs and OH+CO played important roles in OH destruction.Besides,RO2+NO and OH+CO made great contributions to HO2 formation,and HO2 was mainly consumed by the reaction of HO2+NO.（5）Compared to non-O3 episode days,higher simulated O3 production,destruction and net production rates were found on O3 episode days at both sites.The simulated O3 production,destruction and net production rates at ZY were higher than those at HP which suggests that local O3 photochemical formation played a more significant role on O3 levels at ZY.O3 was mainly generated by the reaction of HO2+NO,but O3 was mainly consumed by OH+NO2 at ZY while O（1D）+H2O was the most predominant pathway of the O3 destruction at HP,indicating that there were differences between ZY and HP in the O3 destruction process. |
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