Approaching gas–particle partitioning equilibrium of atmospheric PCDD/Fs with increasing distance from an incinerator: measurements and observations on modeling

A comprehensive sampling campaign was carried out around a municipal solid waste incinerator (MSWI) in central Taiwan in order to evaluate the impact of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) emissions on the ambient air and describe their spatial variation of gas–particle partitioning. Stack flue gas samples from the MSWI were also analyzed to investigate the relationship between the source and the impacted sites. Results showed that the PCDD/F emissions from the MSWI were a major source for PCDD/Fs in the ambient air. Moreover, PCDD/Fs in the ambient air tended to be distributed between the gaseous and particulate phases based on molecular weight; the higher chlorinated congener occupied a higher particulate fraction. There was an increase in the proportion of particle-bound PCDD/Fs with increasing distance from the MSWI. This observation supports the assumption that PCDD/Fs emitted were initially more associated with gaseous phase and the gaseous PCDD/Fs would gradually migrate to particles via either adsorption or absorption process. The results obtained were also applied and compared with the subcooled liquid vapor pressure (PL0)-based model and with the octanol–air partition coefficients (Koa)-based model. These two models were found to be excellent descriptors for the gas–particle partitioning of PCDD/Fs. Regressions for log partition coefficient (Kp) versus log PL0 and log Kp versus log Koa both demonstrated that PCDD/Fs were approaching equilibrium partitioning with increasing distance from the MSWI in the current study.