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 CIPAHs 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-ClBaP differed significantly from that of the other CIPAHs. Comparison of the atmospheric CIPAH concentration profile normalized to 1-ClPy concentration with that or a traffic air sample revealed significant differences between the profiles. The behavior of the atmospheric CIPAHs was also influenced by the origin of the associated particulates, which varied according to season. The positions of chlorination in the detected CIPAHs were consistent with those where the frontier electron density was high. This means that the atmospheric CIPAHs were formed by secondary reactions with chlorine atoms. The photostabilities of the CIPAHs were also investigated in laboratory experiments using a chemical model system. The CIPAHs 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.