The Impact Of Inter-city Transmission On Air Quality In The Yangtze River Delta Region

The Yangtze River Delta(YRD)urban agglomeration is one of the most developed regions in China.During recent decades,this region has experienced severe regional haze and photochemical smog pollution problems.In this study,we used a source-oriented chemical transport model to quantitatively estimate the effects of inter-city transport on fine particulate matter(PM_2.5)and ozone(O₃)among the 41 cities in the YRD urban agglomeration in 2018.we analyzed the transport of pollutants in the Yangtze River Delta.Seasonal characteristics,source contributions of different components,study the relationship between the cumulative contribution of pollutants and distance,and provide insights for regional cooperative controls of PM_2.5 and O₃.The results show that:(1)The inter-city transport in YRD is very obvious,and the local contribution to PM_2.5 is13%?43%.The local contribution of all cities,the contribution of other cities in the YRD and the contribution outside the YRD.The average proportions are 25.2%,32.3%and 42.5%.The annual O₃ contribution from the local area is 11.9%to 43.3%,The average proportions are27.8%,50.0%and 22.4%.(2)For PM_2.5,when pollution occurs,the local contribution decreases,and the contribution from other cities in the Yangtze River Delta increases.In terms of seasons,local contributions are greater in summer and autumn,and transport is stronger in spring and winter.For O₃,when pollution occurs,the contribution of local and other cities in the Yangtze River Delta will increase.It shows that the O₃ pollution in the Yangtze River Delta is mainly generated locally.In terms of seasons,local contributions are higher in summer and autumn,followed by spring,and the least local contribution in winter.(3)The sources of different components of PM_2.5 in YRD are quite different.The local contribution of the secondary PM is significantly less than that of the primary PM,indicating that the primary task of controlling PM_2.5 is to control the local primary PM.The local contribution of SOA is much greater than that of secondary inorganic aerosols.These results indicate that VOC emission controls in local and nearby cities could effectively reduce the SOA concentrations,but reducing the amount of SO₄^2-would require SO₂ emission controls over much larger areas.(4)For PM_2.5,the cumulative contribution is 50%,and 60%corresponds to emissions within a distance of 102 km and 308 km,respectively.To reduce the PM_2.5 concentration of a city in YRD by half,it is necessary to carry out regional cooperative emission control for cities within at least 102 km,because these cities play a leading role in the pollutant concentration of the target city.In the four seasons,under the premise of less cumulative contribution of the same proportion,the reduction of secondary PM requires the control of longer-distance emissions than primary PM.As far as particulate matter is concerned,to achieve the same control goals,a wider range of control is needed in winter.In the four seasons,the impact of local primary PM is greatest in summer,and O₃ in winter is the main contribution in YRD.