Pollution Characteristics Of Ozone And Its Precursors And Contribution To Ozone Generation In Typical Cities Of Sichuan Province In Summer

In recent decades,global ozone（O₃）pollution has become more and more serious.In the polluted weather of many cities in China,the proportion of ozone as the primary pollutant is increasing gradually As a secondary pollutant generated by photochemical reaction,the formation of ozone is affected by solar radiation intensity,meteorological and geographical conditions.The formation of ozone is also associated with air pollutants such as Volatile Organic Compounds（Volatile Organic Compounds,VOCs）and nitrogen oxides（NO_x=NO+NO₂）and have a nonlinear relationship with them.So scientific ozone precursor reduction strategy is very important.In China,studies on the characteristics of air pollution in Sichuan Province,an important province in Southwest China,are mainly focused on Chengdu City,and there are relatively few studies on other cities.Therefore,Leshan City and Panzhihua City,which are typical cities in geographical location and industrial structure,are selected as the research objects in this study.This study was conducted in panzhihua and leshan city from July to August in 2019.Ozone pollution characteristics and its precursor were observed and analyzed through the use of receptor model model（PMF）and photochemical box model based on the observation model（OBM）,and other technical means,to judge the sensitivity between ozone and its precursor and to find out the ozone generated contribute significant precursor and the main emission source.It provides theoretical basis and technical guidance for the formulation of ozone control strategy in Leshan City and Panzhihua City.The main research contents and results are as follows:Through the analysis of the pollution characteristics of ozone and its precursors in two typical cities,it was found that Leshan was surrounded by high terrain,and local circulation had a great influence on the transport and diffusion of pollutants.The wind speed in Panzhihua is relatively high,and it is susceptible to the influence of east wind and spring westerly monsoon for most of the year,so there may be the influence of elevated source transmission between urban stations.The spatial and temporal distribution of the annual ozone concentration in the two cities showed the characteristics of low in urban area,high in suburban area,high in spring and summer,and low in autumn and winter,among which the ozone pollution in Panzhihua City was relatively concentrated in May and August.In both cities,NO_x concentration was high in urban area,low in suburban area,low in summer and high in winter.The concentration of carbon monoxide（CO）in the two cities showed a diurnal trend of double peaks in the morning and evening.In Panzhihua,CO continued to accumulate at night,and the concentrations of other conventional pollutants except ozone were significantly higher than Leshan.In recent years,the ozone pollution in the two cities has gradually deteriorated.During the monitoring period,all kinds of emission sources in the two cities were relatively fixed.The concentration of non-methane total hydrocarbon（NMHCs）in Leshan city showed obvious double peaks in the early and late days,and there was a good negative correlation between NMHCs and ozone in the daytime.During the monitoring period,ozone generation was mainly controlled by VOCs,while the peak production of ozone in the pollution days was controlled by NO_x.During the online monitoring of VOCs in Panzhihua City,NMHCs showed a great diurnal difference,and the negative correlation between NMHCs and ozone was more obvious in the daytime.Most of the ozone generation in the monitoring day was in the VOCs control area,but the sensitivity of ozone to NO_x local generation was improved in the peak period.Seven factors,including diesel/LPG exhaust emission sources,gasoline use and volatilization,fixed combustion,solvent use,plant emissions,industrial raw materials and solvents use and petrochemical emissions,were analyzed by using PMF receptor model.In Panzhihua,there are 8 factors including the use of liquefied petroleum gas,metallurgical industry and combustion emissions,vehicle exhaust emissions,oil and gas volatilization,solvent use,petrochemical emissions,industrial raw materials and solvents use and plant emissions,were analyzed by using PMF receptor model.Motor vehicle emissions and fixed combustion sources are important sources of atmospheric VOCs in Leshan City.The industrial emissions in Panzhihua City are significantly higher than Leshan City,and the contribution of competitive industries is prominent.Metallurgical industry and combustion source related emissions need to be further manipulated and optimized.The sensitivities of ozone generation to precursors in Leshan City were as follows:AVOC>NO_x>BVOC>CO;NO_x>AVOC>BVOC>CO.The relative incremental reactivity（RIR）of NO_x in the two cities was negative.The contribution of plant emission to ozone generation in both cities is far greater than that of other anthropogenic sources.In Leshan City,anthropogenic sources of VOCs related to industrial production to ozone generation is the largest,followed by the use of solvent.In the anthropogenic sources of Panzhihua City,the contribution of VOCs related to industrial production is greater than that of Leshan City,among which the metallurgical industry and combustion sources are the largest sources of industrial sources contributing to ozone,followed by vehicle exhaust sources.The process of producing ozone in Leshan and Panzhihua is dominated by the reaction of superoxide（HO₂）+NO,while the main path of ozone depletion is the formation of HNO₃（OH+NO₂）and the photolysis reaction of ozone.In this study,seven idealized precursor reduction schemes were simulated for two cities.Considering the local actual situation,it is recommended to choose scheme#2（VOCs/NO_x reduction ratio 3:1）for both cities as the best reduction scheme.The anthropogenic sources（motor vehicle sources,fixed combustion sources）,and anthropogenic industrial production（chemical emission and industrial raw material production,etc.）that have the greatest influence on the local generation of ozone in the summer atmospheric receptor environment of Leshan City should be regarded as the key control points of Leshan City.The anthropogenic sources of VOCs in summer atmospheric environment of Panzhihua City are relatively high:various industrial sources,motor vehicle sources and liquefied petroleum gas sources,as well as the anthropogenic sources of metallurgical industry and combustion sources which have the greatest influence on the local generation of ozone should be the key points of urban control of Panzhihua City.