Chlorinated　polycyclic　aromatic　hydrocarbons　(ClPAHs)　have　been　reported　to　be　formed　during　incineration　processes.　Despite　dioxin-like　toxicities　of　ClPAHs,　little　is　known　on　the　occurrence　of　these　chemicals　in　the　environment.　In　this　study,　concentrations　of　24-h　airborne　PM10　and　PM2.5-associated　ClPAHs　and　their　corresponding　parent　PAHs　were　monitored　from　October　2011　to　March　2012　in　a　suburban　area　in　Shanghai,　China.　In　addition,　daytime　and　nighttime　particle　samples　were　collected　for　7　days　in　April　from　the　same　sampling　site.　Twelve　of　twenty　ClPAH　congeners　were　found　in　PM10　and　PM2.5　at　concentrations　ranging　from　2.45　to　47.7　pg/m(3)　with　an　average　value　of　12.3　pg/m(3)　for　PM10,　and　from　1.34　to　22.3　pg/m(3)　with　an　average　value　of　9.06　pg/m(3)　for　PM2.5.　Our　results　indicate　that　ClPAHs　are　ubiquitous　in　inhalable　fine　particles.　The　concentrations　of　Sigma　ClPAHs　and　specific　congeners　such　as　9-ClPhe,　3-ClFlu,　1-ClPyr,　7-ClBaA,　and　6-ClBaP　in　particles　collected　during　nighttime　were　higher　than　those　collected　during　daytime,　which　suggests　not　only　diffusion　of　ClPAHs　in　air　by　atmospheric　mixing　but　also　photochemical　degradation　during　daylight　hours.　Among　the　individual　ClPAHs　determined,　6-ClBaP,　1-ClPyr,　and　9-ClPhe　were　the　dominant　compounds　in　PM10　and　PM2.5.　The　percent　composition　of　6-ClBaP,　1-ClPyr,　7-ClBaA,　and　3-ClFlu　between　PM10　and　PM2.5　was　similar.　Significant　positive　correlations　were　found　between　concentrations　of　ClPAHs　and　their　corresponding　parent　PAHs,　particle　mass,　and　total　organic　carbon　(organic　carbon　plus　elemental　carbon),　indicating　that　ClPAHs　are　sorbed　onto　carbonaceous　matter　of　PM.　Concentrations　of　parent　PAHs　predicted　by　multiple　linear　regression　models　with　PM　mass,　total　organic　carbon,　temperature,　and　relative　humidity　as　variables　reflected　the　measured　concentrations　with　a　strong　coefficient　of　determination　of　0.917　and　0.946　for　PM10　and　PM2.5,　respectively.　However,　the　models　generated　to　predict　ClPAH　concentrations　in　PM　did　not　yield　satisfactory　results,　which　suggested　the　differences　in　physical-chemical　properties　and　formation　processes　between　ClPAHs　and　their　corresponding　parent　PAHs.　7-ClBaA　and　6-ClBaP　collectively　accounted　for　the　preponderance　of　the　total　dioxin-like　TEQ　concentrations　of　ClPAHs　(TEQ(ClPAH))　in　PM　samples.　Exposure　to　toxic　compounds　such　as　ClPAHs　and　PAHs　present　in　PM2.5　can　be　related　to　adverse　health　outcomes　in　people.