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.　Be-tween　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.　(C)　2020　The　Research　Center　for　Eco-Environmental　Sciences,　Chinese　Academy　of　Sciences.　Published　by　Elsevier　B.V.