Study On The Causes Of Ground-level Ozone In Typical Cities Of Yunnan Province

Since the implementation of the new environmental air quality standard in Yunnan Province,the air quality is generally good,but the problem of atmospheric ozone pollution in some areas has already appeared.Therefore,in view of the excessive concentration of ozone in some cities in Yunnan Province,from June 2016 to June 2017,the study monitored VOCs,NOx and O₃ and meteorological data such as wind direction,wind speed,temperature,humidity,and solar radiation intensity in the study areas of Jinghong,Mangshi,and Zhaotong by combining the special geographical conditions and unique climatic conditions of the highland cities and the special geographical conditions as well as unique climatic conditions of the highland cities.a preliminary analysis of the causes of ozone was conducted from the perspective of meteorological factors,ozone precursors,and ozone transport.The comparasion of concentration of O₃ among the study area is:Zhaotong>Mangshi>Jinghong.The concentration of O₃ in Zhaotong is relatively high throughout Yunnan Province throughout the year.The monthly change pattern of the O₃ is consistent with the characteristics of the highest concentration in spring?from March to May?and the lowest concentration in summer.The daily variation of concentration of O₃ is the same,showing a single peak type,with the peak appearing in the afternoon from 15:00 to16:00.The concentration of NO_x in Jinghong and Mangshi is the highest in spring,Zhaotong has the highest concentration in winter,and the best correlation with O₃ in the corresponding season;in spring,NOx has the greatest impact on the formation of O₃ in Jinghong and Mangshi;In winter,NOx in Zhaotong may be affected by civilian coal and motor vehicles,which affects the generation of O₃.The NO_x ranges corresponding to the high values of O₃ in the three cities are quite different.Zhaotong has exceeded the standard in the range of Nox with 5¹70?g/m³,and the impact of fluctuations is relatively large.Mangshi has an exceeding concentration of O₃ in the range of15⁴0?g/m³ and Jinghong in the range of 8²5?g/m³.The NOx concentration decreases as the concentration of O₃ increases in an exponential manner.NO_x has the greatest impact on production of O₃ in Zhaotong,followed by Mangshi and Jinghong.Since the study area is located in the plateau region,the study found that the intensity of UV radiation significantly affects the formation of O₃ and is positively related to the concentration of O₃.In spring,Yunnan is in the dry season,and the radiation intensity in the plateau is strong,resulting in enhanced photochemical reactions in the atmosphere.The impact of concentration of O₃ increases,and the relative humidity is also more obvious,showing negative correlation with concentration of O₃;From the correlation analysis of conventional pollutants in the study area,we can see that there is a good correlation between O₃,NO₂,and CO throughout the entire year in the spring and autumn of Jinghong and Zhaotong.This may be because O₃ is affected by local motor vehicle exhaust and local fossils as well as the combustion of fuel or biomass and the impact of local civilian coal.In the dry season,the comparasion of concentration of urban VOCs is:Jinghong>Zhaotong>Mangshi;and the comparasion of that in rainy season is:Jinghong>Mangshi>Zhaotong.The concentration of VOCs in the dry season is greater than that in the rainy season,and the concentration of VOCs in urban areas is greater than that in the suburbs.The concentration of VOCs in Zhaotong changes greatly during the wet and dry seasons and is significantly affected by rainfall,temperature,and UV radiation intensity.The concentration of VOC Jinghong City has no significant difference between the wet and dry seasons,and the source emission of local VOCs is relatively constant.The main concentrations of VOCs in the study area show that propane,n-butane,isobutane,isopentane,and 3-methylpentane are the main hydrocarbons,and isoprene and propylene are the olefin compounds.The concentration of cis-2-butene is higher;the concentration of benzene,toluene,p-,m-xylene,p-ethyltoluene,styrene and 1,2,4-trimethylbenzene in the aromatic hydrocarbons is more prominent.The changes of VOCs species in the dry and wet seasons are obvious:The impact of 3-methyl pentane,benzene,p-ethylbenzene,and 1,2,4-trimethylbenzene on vehicle identification components is relatively large.Isobutane and propylene are significantly reduced during the rainy season.The ozone generation potential of VOCs in the atmospheric environment of Jinghong and Mangshi is:olefins>aromatic hydrocarbons>alkanes,Zhaotong:olefins>aromatic hydrocarbons>alkanes.The contribution of isoprene,propylene,and cis-2-butene in olefins is the most prominent,and the contribution of toluene and1,2,4-trimethylbenzene in aromatic hydrocarbons is prominent.Isoprene contributes a lot and may be affected by the local natural vegetation emission sources.The contribution of exhaust emissions from motor vehicles such as toluene,propylene,and para-xylene to ozone generation is also prominent.The production of O₃ in Jinghong is more sensitive to precursor VOCs,and VOCs mainly come from the contribution of natural vegetation emission sources in the region;The production of O₃ in Mangshi is more sensitive to precursor VOCs,VOCs are mainly contributed by natural vegetation and external emission sources;The generation of O₃ in Zhaotong is more sensitive to precursor NOx,and is significantly affected by local industrial sources and civil coal combustion.After observing the trajectory maps of the 12 months of the three cities,it can be found that the air mass transmissions in Jinghong and Mangshan mainly come from Southeast Asia,such as Burma,Laos,Thailand,and the Bay of Bengal.The high concentration of O₃ in spring is obviously affected by Transmission Impact of Southeast Asia Fire Point Pollutant.The entire north-central part of Yunnan is in the low ozone area.Jinghong,Mangshi,and Zhaotong are located on the edge of the low-value area.Therefore,the ozone concentration is slightly higher than that in other parts of Yunnan.At the same time,these three areas have ozone input from the surrounding areas,especially in the Zhaotong region,which has strong ozone convergence in the spring.According to the wind field,we have discovered that Zhaotong is affected by atmospheric transmission from surrounding areas for a long period of time,and irregular ozone from the upper layer,so its base value of ozone is higher than that in Jinghong and Mangshi.