Study Of Ozone Pollution Characteristics And Sources In Linfen City,2019-2021

Ground-level ozone（O₃）is one of the important factors causing regional atmospheric compound pollution in China.In recent years,China has gradually incorporated O₃ pollution prevention and control into national air pollution control actions.As a major coke production base in Shanxi Province,a large amount of NO_X and VOCs emitted from the coking industry in Linfen City has led to a significant O₃ pollution problem.This paper analyzes and studies the pollution characteristics of O₃ in Linfen city,the influence of meteorological factors,O₃precursors VOCs and transmission of O₃ based on conventional pollutants,meteorological data,and data from one VOCs monitoring point at six national control points in Linfen city from2019-2021,aiming to provide a scientific basis for the Linfen city government to formulate O₃pollution prevention and control.The overall improvement of O₃ pollution in Linfen city during 2019-2021,MDA8-90th decreased from 204μg/m~3 in 19 years to 197μg/m~3 in 21 years.O₃ pollution days decreased by 22 days compared with 19 years,but the exceedance rate is still as high as 22%.O₃ pollution remains severe.MDA8 shows a monthly trend of high summer and low winter,O₃ exceedance days are mainly concentrated in May-September.O₃ concentration is a typical single-peak daily variation,the peak occurs at 2:00-4:00 p.m.,and high temperature and strong solar radiation on sunny days are more conducive to the photochemical generation of O₃ than cloudy and rainy days.The contribution of O₃ pollution to Linfen city is larger in Chengnan,Tangyao,and Shiwei.Focusing on controlling Chengnan and Shiwei when MDA8 is 160-180μg/m~3 and Tangyao when MDA8 is larger than 90th will help Linfen city to reduce O₃ pollution days.In addition,MDA8 is significantly positively correlated with T_max（R=0.74）and negatively correlated with RH_min（R=-0.49）.When the higher wind speed south wind,T_max>22℃and RH_min<65%,Linfen city is most likely to have O₃ pollution exceeded,and corresponding measures should be taken for O₃ pollution prevention and control.As VOCs are important precursors of O₃,this study analyzed the effect of VOCs on O₃during the two O₃ heavy pollution processes in Linfen City from June 29 to July 9 in 2020 and from June 5 to 12 in 2021 for the frequent occurrence of O₃ heavy pollution in June and July,respectively.The results show that O₃ in Linfen is sensitive to VOCs and shows a daily trend of shift from the morning VOCs control area to the noon-to-evening as NO_X-VOCs synergistic control.The average TVOC concentrations during the two pollution processes are 34.66±19.34μg/m~3 and 39.86±29.89μg/m~3,respectively.And the photochemical consumption of VOCs accounts for its initial 21%and 31%of VOCs,and the percentages of each type of component in the monitored concentrations were alkanes>aromatic hydrocarbons>olefins>alkynes,while the photochemical consumption accounted for the largest percentage of olefins.OFP indicated that ethylene contributed more to O₃ generation,and the OFP calculated based on monitored concentrations than photochemical consumption may have underestimated the contribution of highly reactive species such as 1,3-butadiene to O₃.Naphthalene as a typical tracer in the coking industry OFP is high,and high-value areas occur in the northeast and southeast direction with wind speed of about 4 m/s.O₃ in Linfen urban area is influenced by pollution emissions from coking enterprises in the upwind area.To achieve O₃ concentration standards,emission reduction measures of VOCs/NO_X>1:1 and total reduction>30%should be carried out.Source analysis results of PMF show that VOCs in Linfen mainly come from motor vehicle emission sources,LPG use sources,combustion sources,solvent use sources,and coking sources.The PMF results based on the initial concentration simulation may be more realistic.In addition,the results of each source category OFP indicate that it is recommended that Linfen city government focus on prevention and control of local combustion emissions such as traffic sources,strengthen the control of LPG and solvent use,and continue the energy-saving and emission reduction in coking industry.In addition to photochemical local generation of O₃,transport is another factor affecting O₃ concentration.Linfen City is mainly influenced by the transmission of air masses from the southeast and the local and surrounding regions from May to September 2019-2021.In addition,south such as Xiangfen County and northeast such as Hongdong County have a high possibility of O₃ potential source area,and their pollution emissions from a large number of coking and iron and steel plants contribute highly to O₃ in Linfen City.The government should focus on the control of southward industrial emissions during the high O₃ period in summer.The elevated nighttime O₃ concentration in Linfen City occurs 83 times,which is mainly related to the horizontal transmission of polluted air masses from the south and the vertical transmission of O₃-rich air masses above the mountain top boundary layer When the peak O₃ reaches 80μg/m~3at night,we should pay attention to the possible O₃ exceedance the next day.