Local pollution and the cross-boundary transmission of pollutants between cities have an inevitable impact on the atmosphere.Quantitative assessments of the contribution of transport to pollution in inland and coastal cities are necessary for the implementation of practical,regional,and joint emission control strategies.In this study,the Comprehensive Air Quality Model (CAMx),together with the Weather Research and Forecasting model (WRF),was used to simulate the contributions to pollution of different cities in 2016.The monthly inflow,outflow,and net flux from the ground to the extended layers served as the three main indicators for the analysis of the interactions of PM2.5 transport between adjacent cities.Between inland and coastal cities,the magnitude of inflow and outflow are larger in the former than in the latter.The inflow flux in the inland cities (Beijing and Shijiazhuang) was 10.6 and 10.7 kt/day,respectively,while that in the coastal cities (Tianjin,Shanghai,Hefei,Nanjing,and Hangzhou) was 9.1,3.3,5.8,4.4,and 3.7 kt/day,respectively.In terms of variation over the year,the strongest inflow in the BTH region occurred in April,followed by October,July,and January,while that in the coastal cities in YRD occurred in January,followed by October,April,and July.Therefore,based on the flux intensity calculations and the transport flux pathways,effective joint control measures can be provided with scientific support,and a better understanding of the evolutionary mechanism among inland and coastal cities can be acquired.