Atmospheric PCDD/F measurement in Taiwan and Southeast Asia during Dongsha Experiment

The international campaign of Dongsha Experiment was conducted in the northern Southeast Asian region during March-May 2010. To address the effects of long-range transport on the persistent organic pollutants and further understand the PCDD/F contamination in Vietnam, atmospheric PCDD/Fs were evaluated at a coastal station (Pingtung County, Sites A) in southern Taiwan, remote island station in South China Sea (Dongsha Island, Site B) and coastal station (Da Nang City, Site C) in central Vietnam during different sampling periods in this study. The measurements indicated that the atmospheric PCDD/F concentrations were 1.01-27.4fg I-TEQ/m³ (n=22), 1.52-10.8fg I-TEQ/m³ (n=17) and 23.4-146fg I-TEQ/m³ (n=16) at Sites A, B and C, respectively, during different periods in 2010. In March 2010, an Asian dust storm (ADS) that originated in Gobi deserts eventually reached populated areas of East Asia, including Taiwan and the island in northern South China Sea. During the ADS episode, measurements made in southern Taiwan and South China Sea on 16 and 21 March 2010 indicate that the atmospheric PCDD/F concentration increased 6.5 and 6.9 times at Sites A and B, respectively. Furthermore, the significantly higher PCDD/F concentrations and contents in suspended particles (134-546pg I-TEQ/g-TSP) were measured at Site C in the central Vietnam. In addition, the distribution of PCDD/F congeners measured in Central Vietnam was quite different from those measured at other stations with high PCDD distribution (>80%) especially in OCDD (>70%). During the Vietnam conflict, United States (US) forces had sprayed a greater volume of defoliant with higher PCDD/F contents than originally estimated. We consider that the high fraction of PCDDs observed in Vietnam probably originated as anthropogenic emission from specific source in Vietnam.