Measurement of PCDD/F congener distributions in MWI stack gas and ambient air in northern Taiwan

To meet the emission standards that become more and more stringent, the waste incinerators are commonly equipped with various air pollution control devices. Gas/particulate phase distribution of polychlorinated dibenzo-p-doxin and furan (PCDD/F) in stack gas could be much different when different control technologies are applied. This study evaluates PCDD/F congener distributions at the stack gas of a municipal waste incinerator (MWI) and ambient air in northern Taiwan via stack gas and ambient air sampling and analysis. Ambient air samples were taken in the vicinity area of a large-scale MWI for measuring PCDD/F concentrations and partitioning gas/particulate phase from November 1999 through January 2001. Stack gas samples of the MWI were taken during the period of ambient air sampling. The PCDD/F concentrations measured in fall and winter seasons are significantly higher than those measured in summertime. In addition, the results obtained on gas/particulate partitioning of ambient air samples indicate that the particulate-phase PCDD/Fs account for more than 80% of the total concentration. Nevertheless, the gas/particulate partitioning of stack gas PCDD/F sample was completely different from that of the ambient air samples. The gas-phase PCDD/Fs account for more than 85% of the total concentration in MWI stack gas. This study also indicates that as the chlorination level of PCDD/F congeners increases, the percentage of PCDD/Fs existing in gas phase decreases in either ambient air or stack gas of MWI. Furthermore, the temperature in ambient air also affects the percentage of particle-bound dioxins. As the ambient air temperature decreases by 10°C, the percentage of PCDD/Fs in particulate phase increases around 20%. PCDFs account for about 80% of the I-TEQ concentrations for stack gas and ambient air sample, among them the 2,3,4,7,8-PeCDF is the major contributor, accounting for 30–55% of the total I-TEQ.