Chlorinated polycyclic aromatic hydrocarbons in the atmosphere: seasonal levels, gas-particle partitioning, and origin.

Ambient concentrations of 26 chlorinated polycyclic aromatic hydrocarbons (CIPAHs) with 2- to 5-rings were investigated in a Japanese urban city from December 2004 to December 2005. All the targeted CIPAHs were detected in either the gaseous or particulate phase. During the study, the ambient (gaseous + particulate) concentration of total CIPAH ranged from 18 to 330 pg m(-3). The concentrations of gaseous CIPAHs tended to be 2 approximately 100 times higher than those of particulate CIPAHs. A seasonal variability of both gaseous and particulate CIPAH concentrations was observed, with higher concentrations in winter than in summer. A compositional analysis also showed a characteristic trend: relatively low molecular weight CIPAHs dominated in warmer seasons, and high molecular weight CIPAHs dominated in colder seasons. For some CIPAHs, temperature dependence of gas-phase concentrations was statistically significant (p < 0.05), and temperature accounted for 27-63% of the variability in their concentrations. The natural logarithm of total concentrations of particulate CIPAHs were significantly correlated (p < 0.05) with the reciprocal mean temperatures, but not for gaseous CIPAHs, suggesting that there are differences of the sources and ambient fates between gaseous and particulate CIPAHs. Back trajectory analyses suggested that air masses, originating from China, were associated with the highest CIPAH concentrations.