Ozone　(O3)　pollution　in　city　level　is　a　complex　issue　that　arises　not　only　from　local　photochemistry　process　but　also　involves　mid-　or　long-range　O3　transport.　In　this　study,　we　developed　a　modeling　approach　to　dynamically　quantifying　local　photochemical　process　(indicated　as　Chem_O3)　and　estimating　its　role　in　surface　O3　pollution　in　city　level.　The　work　was　conducted　on　North　BTH　of　China　for　summer　of　2022　and　mainly　focused　on　the　urban　areas,　in　which　surface　O3　usually　as　the　most　dominant　air　pollutants　to　harm　population　health.　The　method　was　constructed　via　establishing　the　hourly　response　of　locally-formed　O3　to　locally-released　NOx　(R　O3-NO2　,　ppb　&　sdot;ppb-1)　based　on　ISAM　simulations　and　then　combining　R　O3-NO2　and　ambient　NO2　levels　to　quantify　time-　varying　Chem_O3.　The　results　showed　that　the　monthly　mean　of　Chem_O3　and　its　proportion　to　actual　O3　(Chem%)　was　17.9-26.0　ppb　and　46.7%-62.6%　in　major　urban　areas　of　North　BTH,　following　the　order　of　mega-　city　＞　industrialized　city　＞　normal　city　＞　forest　city.　Moreover,　daily　Chem%　presented　the　different　trend　with　daily　O3　in　these　study　areas,　slight-positive　for　mega-cities,　but　moderate　or　strong-negative　for　most　other　cities.　Specially,　our　developed　method　could　additionally　disentangling　O3　physical　transport　among　the　studied　cities,　and　we　found　the　inflow　of　O3　was　much　lower　than　the　outflow　of　O3　for　two　mega-cities,　while　it　was　opposite　in　other　cities.　We　think　this　method　could　clearly　point　out　the　role　of　local　photochemistry　control　in　O3　reduction,　which　could　help　city　environment　managers　to　develop　scientific　and　effective　policy　strategies　to　cope　with　ozone-related　problems.