Analysis Of Causes And Sources Of Ozone Pollution In Rizhao Based On CMAQ And HYSPLIT Models

In recent years,O₃pollution has become a key factor restricting the further improvement of air quality in our country.As a typical coastal city,the concentration of PM₁₀and PM_2.5in Rizhao has shown an obvious decreasing trend in the past five years,while the number of days when O₃is the primary pollutant is the most among the six basic pollutants since 2017,and has an increasing trend.In order to explore the causes and sources of O₃pollution in Rizhao,on the basis of analyzing the temporal and spatial variation characteristics of O₃pollution,the contribution of O₃and precursors to different physicochemical processes,different source areas and local sources is quantified by IPR process analysis and ISAM source tracking tool,and the difference between exceeding and non-exceeding O₃days is compared.Combined with HYSPLIT model,the regional transport path of O₃in Rizhao was explored.This paper provides reference for formulating O₃control countermeasures in Rizhao and cities in coastal areas.The main conclusions of this study are as follows:（1）The concentration of O₃in Rizhao presents a"bimodal"monthly variation,with the peak value appearing in June and September,and O₃exceeding standard days distributed from April to October.In terms of spatial distribution,O₃concentration decreases from northwest land to southeast coast in June and July,and in September,concentration in coastal areas is higher than that in inland areas.（2）The transport process has a major contribution to the O₃pollution in Rizhao.In June and July,the contribution of O₃in the transport process at 0～60m above the ground is about twice that of the O₃contribution of the photochemical reaction.In September,the O₃contribution of the transport process is more significant,about 4times that of the photochemical reaction.In July,the negative contribution of O₃in the sedimentation process is the most significant,which is 66%higher than that in June,which is also the main reason why the concentration of O₃in July is lower than that in June.The O₃contribution of superstandard solar chemical reactions and transport processes at 0～60m above the ground is greater than that of non-superstandard days.（3）Local sources were the main sources of NO_xand VOCs in Rizhao,with contribution rates of 45.23%and 56.06%,respectively.The main source of O₃is the out-of-area transmission（55.23%）,and the contribution rate of O₃from local sources in Rizhao is 13.47%.Among the surrounding areas,Linyi,Lianyungang and the southern region have great contributions to O₃and its precursors,and the contributions are more significant when the O₃exceeds the standard.The average contribution rates of Linyi,Lianyungang and the southern region to O₃are 1.62%,3.02%and 2.62%,respectively.Among local sources,fossil fuel fixed combustion source is the largest contributor of NO_x（26.84%）,followed by process process source（15.97%）.Process process source was the largest contribution source of VOCs（21.62%）;Mobile source and process source are the main contribution sources of O₃,which are 4.47%and 4.01%,respectively.（4）The transportation paths of O₃and its precursors in Rizhao vary in different months,but the main transportation paths mostly originate from the west and south of Rizhao.The proportion of southern paths is greater than that of western paths,and the trajectories from the eastern Yellow Sea have less transportation of O₃and its precursors.Under the transmission conditions corresponding to shorter trajectories,the O₃contribution rate of local sources in Rizhao will significantly increase.