|Abstract: ||In this study, atmospheric deposition of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in the ambient air of a municipal solid waste incinerator located in southern Taiwan was investigated. A total of 28 ambient air samples and 28 soil samples were taken and analyzed for PCDD/Fs during November 2004 and July 2005.
In order to estimate the gas-particle partitioning of PCDD/Fs in the atmosphere, the correlation between gas-particle partitioning of PCDD/Fs and subcooled liquid vapor pressure which was first established by Eitzer and Hites (1988) (erratum 1998) and revised by Hung et al. (2002) was used. In addition, a complete dataset on the gas-particle partitioning of PCDD/Fs in Taiwan reported by Chao et al.(2004) was also used in this study.
The data shows that the congeners of PCDD/Fs with higher chlorine numbers will have higher fraction of particle phase. For the congener with lower chlorine number, such as 2,3,7,8-TCDD and 2,3,7,8-TCDF, gas phase contributed for 64 to 98% and 73 to 98% to the total, respectively. For the congeners with a higher chlorine number, such as OCDD and OCDF, particle phase contributed for 95 to 100% and 92 to 100% to the total, respectively.
The mean dry deposition fluxes of PCDD/Fs in the ambient air contributed by the gas phase and particle phase were 0.37 and 22 pg I-TEQ m-2 day-1, respectively, and 98.3% was contributed by particle-phase deposition. These results demonstrate that the dry deposition of PCDD/Fs was primarily contributed by the particle phase. With respect to wet deposition, the dissolved and particle phase PCDD/F concentrations in rainwater were 0.168 and 2.24 pg I-TEQ L-1, respectively, and the particle phase contributed for 93%. The total deposition flux of PCDD/Fs was 10.1 ng I-TEQ m-2 year-1, and wet deposition contributed only for 34% to the total. Above results reveal that dry deposition is more important than wet deposition for atmospheric deposition.
Finally, the PCDD/F congener profile of atmospheric deposition was compared to that of soil (shown in Fig. 1). It reveals that most congeners present in atmospheric deposition disappear in soil, except for OCDD. Obviously OCDD is more persistent in the environment than other substances after the effects of vaporization, biodegradation and photodecomposition.