Atmospheric trace elements and Pb isotopes at an offshore site, Ieodo Ocean Research Station, in the East China Sea from June to October 2015

초록

East Asia, especially China, has become a major anthropogenic source region of trace elements due to the rapid industrialization and urbanization in the past decades. Numerous studies reported that anthropogenic pollutants from East Asia are transported by westerly winds during winter to spring across the Pacific to North America and beyond. Here we report elemental concentrations and Pb isotope ratios in airborne particles from Ieodo Ocean Research Station (IORS) located in the middle of the East China Sea (32.07 N, 125.10 E). A total of 30 aerosol samples (PM ) were collected between 18 June and 30 October 2015 and analyzed for trace elements (Zn, As, Mo, Cd, Sb, Ba, Tl, and Pb) and Pb isotopes using ICP-SFMS and TIMS, respectively. The mean concentrations of trace elements ranged from 0.06 ng m for Tl to 10.1 ng m for Zn. These values are much lower (up to several orders) than those at unban sites in East Asia, confirming a low level of air pollution at IORS due to the remoteness of the site from major sources of anthropogenic pollutants. On the other hand, the mean crustal enrichment factors, calculated using Ba as a conservative crustal element, are much higher than unity (84 for Tl, 100 for Mo, 140 for Pb, 166 for Zn, 262 for As, 526 for Cd, and 570 for Sb, respectively), indicating that these elements are of anthropogenic origin. Combining the Pb isotope ratios and the HYSPLIT model 5day backward trajectory analysis, we have identified episodic longrange transport of air pollutants from diverse source regions of China, Korea, Japan and Taiwan to the site in summer (June to August). By comparison, an increasing longrange transport of pollution from China was observed in autumn (September and October). Finally, our study shows that IORS is an ideal background site for monitoring levels of concentrations and source origins of atmospheric trace elements in East Asia.