Occurrence, profiles, and photostabilities of chlorinated polycyclic aromatic hydrocarbons associated with particulates in urban air.

The atmospheric levels of 12 chlorinated polycyclic aromatic hydrocarbons (ClPAHs) associated with particulates at an urban site in Japan were investigated. Only 7 of the 12 species studied were detected in air samples collected monthly during 2002. 1-Chloropyrene (1-ClPy) was detected at the highest concentration (7.5 pg m(-3) (annual mean)), followed by 6-chlorobenzo[a]pyrene (6-ClBaP; 5.6 pg m(-3)) and 9,10-dichlorophenanthrene (5.1 pg m(-3)). The concentrations of the ClPAHs tended to be higher in winter than in summer, with the exception of the 6-ClBaP concentration, which was high in both summer and winter. Correlation analysis also indicated that the behavior of 6-CIBaP differed significantly from that of the other ClPAHs. Comparison of the atmospheric ClPAH concentration profile normalized to 1-CIPy concentration with that for a traffic air sample revealed significant differences between the profiles. The behavior of the atmospheric ClPAHs was also influenced by the origin of the associated particulates, which varied according to season. The positions of chlorination in the detected ClPAHs were consistent with those where the frontier electron density was high. This means that the atmospheric ClPAHs were formed by secondary reactions with chlorine atoms. The photostabilities of the ClPAHs were also investigated in laboratory experiments using a chemical model system. The ClPAHs decayed according to first-order reaction rate kinetics, with photostabilities increasing in the order 6-ClBaP < 1-ClPy < 7-ClBaA < ClPhe < ClFluor, consistent with the trend for the parent PAHs. The photolyses of chlorophenanthrenes and 7-chlorobenz[a]anthracene were confirmed to proceed by initial abstraction of chlorine, followed by oxidative degradation.