Abstract
Dry deposition is one of the major routes by which air pollutants enter the ecosystem, and thus this study investigated the dry deposition characteristics of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and biphenyls (PCBs) in the ambient air of industrial, urban, and rural areas in southern Taiwan from November 2010 to May 2011. Average dry deposition fluxes of total PCDD/Fs and PCBs in the ambient air of four sites were 157-544 pg/m2-day (8.30-27.5 pg ITEQ/ m^2-day) and 289-1010 pg/m^2-day (0.540-1.94 pg WHO-TEQ/m^2-day), respectively. The results showed that particle phase depositions dominated the dry deposition processes for the removal of PCDD/Fs and PCBs from the atmosphere, and the atmospheric deposition flux in the cold season tended to be higher than that during the warm season. The dry deposition velocity of individual PCDD/Fs (0.031-0.546 cm/s) increased as the number of chlorinated substitutes increased, which were similar to those measured or predicted in other Asian countries. Similar patterns of dry deposition velocities were observed for individual PCBs (0.069-3.38 cm/s), due to the fact that low chlorinated PCBs are predominant in gas phase and have lower deposition velocities.
Highlights
Polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and biphenyls (PCBs) are persistent, lipophilic, and bioaccumulative semivolatile organic compounds (SOCs) that are classified as hazardous air pollutants (HAPs) by the USEPA
Similar patterns of dry deposition velocities were observed for individual Polychlorinated biphenyls (PCBs) (0.069–3.38 cm/s), due to the fact that low chlorinated PCBs are predominant in gas phase and have lower deposition velocities
The above results revealed that the atmospheric concentrations were similar to the results of Wang et al (2003), which indicated that total PCDD/F concentrations in ambient air samples collected from a background area, a rural area, a residential area, an urban area, an industrial area, and the vicinity of a crematory in Taiwan were 0.006, 0.023, 0.050, 0.093, 0.190, and 0.521 pg I-toxic equivalent (TEQ)/Nm3, respectively
Summary
Polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and biphenyls (PCBs) are persistent, lipophilic, and bioaccumulative semivolatile organic compounds (SOCs) that are classified as hazardous air pollutants (HAPs) by the USEPA. Since PCBs are chemically similar to PCDD/Fs, the formation mechanisms of PCBs are similar to those of PCDD/Fs via de novo synthesis and/or the thermolysis of precursor compounds which interacted with metallic catalysts (Chin et al, 2012; Wang et al, 2012). PCDD/Fs have been detected in the emissions from waste combustion, chemical plants, thermal sources, metal smelting processes, and vehicles (Chung et al, 2010; Chen et al, 2011; Chiu et al, 2011; Kao et al, 2011; Kuo et al, 2011). As for PCBs, they have been released into the environment by primary (e.g., vaporization or burning of products containing PCBs) and secondary emission sources (e.g., revolatilization from soil, vegetation, water, and air) (Breivik et al, 2002; Yeo et al, 2004).
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