Atmospheric Deposition of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans at Coastal and High Mountain Areas in Taiwan

Atmospheric deposition is of great importance for the sink of air pollutants to the environment, either from local sources as well as coming from long range transport. To further understand the combined impact of both long-range transport from South East Asia and local emission sources of pollutants, the characteristics of polychlorinated dibenzo -p- dioxins and dibenzofurans (PCDD/Fs) in the ambient air of two background sites in Taiwan namely, Hengchun (coastal area) and Lulin (high mountain area), were simulated by regression of PM 10 versus total-PCDD/F mass concentration, modeling of gas-particle partitioning, and simulations of both dry and wet deposition. The simulated PCDD/F concentrations at Hengchun, ranged between 0.0039–0.0106 and 0.0054–0.0138 pg WHO 2005 -TEQ m −3 for 2012 and 2013, respectively. For Lulin site, the PCDD/F concentrations ranged between 0.0016–0.0029 and 0.0016–0.0032 pg WHO 2005 -TEQ m −3 for 2012 and 2013, respectively. The WHO 2005 -TEQ ratios of PCDDs to PCDFs at both sites were less than unity, indicating that PCDF dominated the total toxicity. The results show that higher chlorinated PCDD/Fs primarily present in particulate phase for all seasons at both sampling sites especially in winter. Average dry deposition fluxes at Hengchun (57.1 pg WHO 2005 -TEQ m −2 month −1 ) were approximately 5.1 times higher than those at Lulin (11.2 pg WHO 2005 -TEQ m −2 month −1 ). The annual average dry deposition velocities were estimated to be 0.28 and 0.22 cm/s for Henchun and Lulin, respectively. For the whole period (2012–2013), the mean monthly wet deposition fluxes at Hengchun (averaged 11.7 pg WHO 2005 -TEQ m −2 month −1 ) were 1.44 times higher than that at Lulin (averaged 8.11 pg WHO 2005 -TEQ m −2 month −1 ). The calculated annual average total-PCDD/Fs-WHO 2005 -TEQ concentrations in the rain were 0.064 and 0.027 pg WHO 2005 -TEQ L −1 for Henchun and Lulin, respectively. The estimated annual average scavenging ratios of total-PCDD/Fs-WHO2005-TEQ were 8015 and 13450 for Henchun and Lulin, respectively. Similarly, for the entire study period (2012–2013), the average annual total (dry + wet) deposition flux of total PCDD/Fs-WHO 2005 -TEQ in the terms of pg WHO 2005 -TEQ m −2 year −1 at Hengchun (824.9) was 3.5 times higher than those in Lulin (232.0). On the basis of total PCDD/Fs-WHO 2005 -TEQ, the mean fraction contributed by dry deposition at Hengchun were 78.2% and 78.9% in 2012 and 2013, respectively, while at Lulin the avera