Prediction of gas/particle partition quotients of Polybrominated Diphenyl Ethers (PBDEs) in north temperate zone air: an empirical approach

Gas/particle (G/P) partitioning process is an important factor governing the transport and fate of chemicals in the atmosphere. Based on a large dataset of more than 700 pairs of air samples in gaseous and particulate phases with a wide ambient temperature range of 60°C from -22°C to +38°C obtained from our Chinese POPs Soil and Air Monitoring Program, Phase 2 (China-SAMP-II), we investigated G/P partitioning behavior of polybrominated diphenyl ether (PBDEs) in Chinese air. We derived for the first time empirical equations to predict the values of slopes and intercepts for both subcooled-liquid-vapor-pressure (PL)-based and octanol-air-partition-coefficient (KOA)-based models as functions of temperature, and thus predicted partition quotient (KP) without assuming an equilibrium status and free of artifacts. These equations have been successfully applied to predict the values of KP for PBDEs in air of China and other countries in the north temperate zone (NTZ) and also at an Arctic site in East Greenland, and our results matched the monitoring data well at background, rural, urban, and suburban sites, but not at e-waste sites due to the unpredictable PBDE emissions at these sites. Our equations predicted that the ranges of slopes were 0.02-0.82 for logKP-logKOA plots and -0.82 to -0.02 for logKP-logPL plots at temperatures ranged of 60°C from -22°C to +38°C. Our new KOA-based equation was compared with the Harner-Bidleman equation that was derived at a condition of equilibrium, and the results indicated that our new equation has a better performance than the Harner-Bidleman equation in describing G/P partitioning behavior of PBDEs in air as functions of logKOA. We also found for the first time that the G/P partitioning of PBDE congeners would become saturated in the particulate phase respect to the gas phase if the ambient temperature is low enough. A criterion to classify the equilibrium and nonequilibrium status for PBDEs was also established using logKOA. The study presented in this paper provides a useful tool for environmental scientists in both monitoring and modeling research on G/P partitioning behavior for PBDEs in air.