Observation And Modeling Studies Of Haze Pollution And Regional Transport Over Wuhan Area

As a key metropolitan area in the Yangtze River middle reach,serious haze pollution of Wuhan needs to be further researched.To investigate characteristics of air quality change and haze pollution,meteorological factor of affecting pollutants and meteorological conditions during the typical heavy pollution events in winter respectively,by fully using observation data of amibient pollutant and meteorological elements.Besides,the FLEXPART-WRF model simulation experiment from 2008 to 2017 combined with the spatial distribution of ambient pollutant emission intensity were carried out,the climate characteristics of PM_2.5“influence domains”over the Wuhan area were revealed,and the relative contribution of reginal transport and local emissions to PM_2.5 was evaluated in the past 10 years.The major work of this thesis is summarized:1)Characteristics of air quality and haze pollution over Wuhan area in recent years and their meteorological effectsThe daily variation of PM_2.5,PM₁₀,CO and NO₂ were double-peak distribution,while SO₂ and O₃ showed a significant single-peak characteristic.The concentration of PM_2.5,PM₁₀,CO and SO₂ of industrial zone in the edge of Wuhan city is higher than the city center,the highest concentration of NO₂ is located in the residential zone in urban centers,and spatial distribution of O₃ is higher in rural areas than in urban areas.The proportion of PM_2.5pollution days in Wuhan decreased from 2015 to 2018,while the level of air pollution is still severe,especially in winter.The pollution events in Wuhan are easily to occur at night and dissipate after sunrise,while heavy pollution events were occured frequent at any time,and which characterized with short duration,rapid outbreak and dissipation.Meteorological conditions play an important role in the variation of PM_2.5 concentration over Wuhan,especially temperature,humidity,wind speed and precipitation.High PM_2.5 concentration is easy to occur with big-wind meteorological conditions in spring,autumn and winter,while it is easy to occur under high-temperature in summer.The precipitation of moderate rain and above level are beneficial to scavenging PM_2.5,while that of light rain is contributed to increasing PM_2.5 concentration.2)The pollution characteristics and meteorological conditions during a typical heavy pollution process in winter over Wuhan areaIn January 2016,Wuhan were suffered a twenty-one continuous days PM_2.5 pollution process,including three heavy pollution events,which were characterized by short duration,rapid outbreak,and rapid dissipation.The significant chemical compositiones of PM_2.5 in Wuhan are NO^3-,SO₄^2-and NH₄⁺,the formation of heavy pollution events is also highly related to the increasing of theoe three components,especially the concentration of SO₄^2-.The meteorological conditions of the three heavy pollution events are different from the major haze-polluted areas in China over Wuhan in January 2016,there was a“non-stagnation”meteorological condition,namely,the wind speed increases and the atmospheric static stability decreases.Reginal transport play an ipmortant role in the variation of ambient pollutant concentration during the three heavy pollution events in January 2016,and the regional PM_2.5 transport contributed over 62%.The mainly source area of pollutant loacted in the northern neighboring provinces,especially from Henan,Anhui,Shandong,Jiangsu and Hebei provinces.3)Contribution of regional transport to haze pollution over Wuhan and Climate Characteristics of PM_2.5“influence domains”The 10-year FLEXPART-WRF simulation indicate that PM_2.5“influence domains”of Wuhan can be divided into the local sources of Wuhan and its urban circle,as well as the exogenous source in the surrounding areas of Anhui,Henan and Hunan.The contribution of local emission is 54.1%,where is the most important and stable“influence domain”of ambient pollutants in Wuhan,and the regional transport contribution from outside Hubei Province accounts for 42.9%.The contribution of regional transport to PM_2.5 in Wuhan is similar to the local emission.Wuhan is likely to be an important acceptance area of ambient pollutants in its neighboring provinces.There is a significant contribution of regional transport in winter,and the ambient pollutants mainly come from two regional transport channels,the northern channel（along the low hills in the west of the Dabie Mountains）and the east channel（along the Yangtze River channel）.