A　one-year　observation　of　atmospheric　peroxyacetyl　nitrate　(PAN)　in　the　border　of　Beijing-Tianjin-Hebei　(BTH)　was　conducted　during　2018-2019　to　assess　the　photochemical　pollution　in　this　region.　PAN　daily　average　was　2.23,　3.72,　5.34　and　2.44　ppb(v)　in　October,　January,　April　and　July.　The　higher　PAN　here　compared　to　previous　studies　on　urban　Beijing　implies　the　deterioration　of　photochemical　pollution　in　BTH　region.　High　positive　correlation　between　PAN　and　CO　in　October　and　January　points　to　the　important　role　of　tropospheric　accumulation　in　PAN　level　in　fall　and　winter;　while　Delta　O-3/APAN　analysis　implies　that　the　photochemical　pollution　was　more　aged　in　this　border　than　in　urban　Beijing,　and　more　aged　in　October　than　in　April.　Based　on　the　calculations　of　PAN　photochemical　formation　and　thermal　decomposition,　PAN　yield　rate　was　determined,　0.20,　0.07,　0.47　and　0.08　ppt.s(-1)　for　daily　average,　0.87,　0.32,　0.95　and　0.93　ppt.s(-1)　for　daily　maximum,　respectively　in　October,　January,　April,　and　July.　Local　photochemical　pollutions　still　existed　in　the　border　of　BTH　in　non-winter　seasons.　Potential　source　contribution　function　analysis　(PSCF)　found　that　the　grids　that　most　potentially　contribute　to　high　PAN　appeared　around　the　border　site　in　July,　50-100　km　away　in　direction　of　southwest　in　January,　both　around　this　site　and　along　the　southern　trajectory　clusters　in　October　and　April.　Transport　of　PAN　from　South　Hebei　and　Tianjin　to　Beijing　could　be　seen　in　non-summer　seasons.　Regression　analyses　further　quantified　the　contribution　of　regional　transport　to　PAN　in　the　border,　roughly　65%　(April　and　October),　93%　(January)　and　48%　(July)　at　noon　time.　Finally,　the　comparison　in　PAN　during　12:00-16:00　under　various　winds　explores　the　more　severe　photochemical　pollutions　in　South　Hebei　and　Tianjin　compared　to　Beijing　in　non-summer　seasons,　but　the　same　level　of　photochemical　pollutions　in　various　cities　of　BTH　in　summer.