Study On The Causes And Variations Of Ozone Pollution In Zhengzhou City From 2014 To 2020

In recent years,with the level of surface O3 concentration showing an upward trend in China,the issue of serve O3 pollution has been getting more and more attention.Analyze the cause of O3 pollution plays an important role in the prevention and control of regional O3 pollution.Taking Zhengzhou as an example of central cities,the characteristic of O3 pollution,meteorological influences,the nonlinear relationship of O3 formation with its precursors,and photochemical process were analyzed closely around the above several aspects,to effectively analyze the cause of local O3 pollution.Firstly,based on the online monitoring data of air quality and meteorological parameters from 2014 to 2020,in this study,the long-term variations of O3 and Ox was studied,and found the 90th percentile of O3 MDA8 were increased in an urban and suburban area with 12.04 μg·m-3·a-1 and 9.13 μg·m-3·a-1,respectively.The upward trends of O3 and the Ox implied the atmospheric oxidation capacity is increasing.The monthly variation of O3 and NOx in different type stations were M and V type.Compared to working days,the weekend shows the anti-weekend effects.The diurnal variation of O3 and NOx were singly and double-peak diurnal cycles,the daily maximum O3 concentration at each station showed rural sites>suburban>urban>industrial>traffic.The maximum value of dO3/dt reaches 10:00,and the suburban station reaching a maximum value of 9～11 ppb·h-1.Secondly,O3 concentration is positively correlated with air temperature,and negatively correlated with relative humidity,pressure,and NOx.The nonlinear relationship between O3 concentration and wind speed by SPSS and wind rose.As for the urban station,when the hourly temperature(T)exceeded 23℃,relative humidity(RH)was less than 65%,and the wind direction was southwest and southeast,the exceedance probability of the O3 concentration was relatively higher.The main controlling factors of city and industrial site also are T and RH,traffic and suburb site also are T and WS.Back trajectory analysis and potential sources of O3 in different seasons were significantly different.And the high O3 concentration in summer was mainly affected by the local photochemical formation and regional transport from Hebei,Shandong,and Anhui.The case of O3 pollution showed that the increase of precursor emissions and the high-pressure ridge lead to excessive O3 concentration together.Thirdly,the results of the smog production model indicated that O3 production in Zhengzhou mostly presents VOCs-limited,and the transition regime and NOx-limited regime were also found for the suburb and rural stations.The result of the Observationbased model(OBM)combine with the relative incremental reactivity was to investigate the O3-VOC-NOx relationship and found shows municipal environmental monitoring station presents VOCs-limited from May to September.The analysis of different periods such as the O3 non-pollution period,O3 continuous pollution period,and O3 pollution climbing period shows that strong solar radiation,high temperature,low humidity,and low pressure lead to excessive O3 concentration.Plant emissions and motor vehicle activities are relatively enhanced,while industrial,solvent,and fuel combustion activities are relatively reduced during the O3 pollution period.The mean mixing ratio of alkanes is the largest contributor to TVOCs,followed by halocarbons,OVOC,aromatics,alkenes,and alkyne.The alkenes and aromatics species are dominant role species for controlling O3 pollution were analyzed according to LOH contribution rate and O3 generation potential(OFP).And the VOCs-limited and transition regimes appear alternately,with alkenes and reactive aromatics played a significant role in O3 formation.Finally,the OBM model was used to analyze the concentration levels of OH and HO2 radicals,HOx radicals budget,and in-situ O3 photochemistry.Results show the O3 production was found to be major from the reaction of HO2 radicals and NO,and the reaction of OH radicals and NO2 was the major contributor to O3 destruction.The OH radicals are mainly generated from the reaction of HO2 radicals and NO,and are mainly removed from the reaction of the OH radicals with VOCs,CO,and NO2.The HO2 radicals are generated from the reaction of OH radicals and HCHO,with the photolysis of HCHO.And HO2 radicals were removed by the reaction of HO2 radicals with NO and RO2 radicals,the termination reaction of HO2 radicals.Higher average Net(O3)rate(4.78 ppbv h-1),the higher concentration of OH(4.77 molecule cm3×106),and HO2 radicals(7.72 molecule cm-3×108)were found in consecutive O3 polluted period.The empirical kinetic modeling approach(EKMA)demonstrated that O3 formation tends to be a VOC-limited region in Zhengzhou,and 2020 was closer to the transition regime.The ridge line of the EKMA curve shows VOCs/NOx=3:1 can efficiently control O3 pollution.