Trace elements and Pb isotopes in aerosols (PM10-2.5) at Ieodo Ocean Research Station in the East China Sea from 2015 to 2016

초록

The East Asian region, especially China, is a large and growing source of atmospheric emissions of anthropogenic trace elements due to the rapid industrialization and urbanization. These pollutants are well known to be transported over long distance to the North Pacific and beyond, particularly during winter to spring due to the prevailing westerly winds. Long-term air quality monitoring at a background site is thus required to characterize temporal trend of atmospheric concentration levels and sources of anthropogenic trace elements in East Asia. In this study, we collected aerosol samples at Ieodo Ocean Research Station (IORS) located in the middle of the East China Sea (32.07o N, 125.10o E) between June 2015 and September 2016 (82 aerosol samples in total) for two size ranges of 10-2.5 μm (PM10-2.5). All samples were analyzed for trace elements (Cu, Zn, As, Mo, Cd, Sb, Tl and Pb) and Pb isotopes using inductively coupled plasma sector field mass spectrometer (ICP-SFMS) and thermal ionization mass spectrometry (TIMS), respectively. The mean concentrations of atmospheric trace elements at IORS range from 0.045 ng m-3 for Tl to 13.86 ng m-3 for Zn, which are observed to be significantly lower than those reported from various sites in East Asian countries mainly due to the remoteness from source regions. By comparison, the mean crustal enrichment factors, calculated using Al as a conservative crustal element, show rather high values between 124 for Tl and 2245 for Sb, indicating a significant input of anthropogenic pollutants to the site. The seasonal trend of Pb isotopic composition shows a relatively smaller variation in 206Pb/207Pb ratio from autumn to spring compared to summer. Combining Pb isotopic signatures and the HYSPLIT backward trajectories determined for each sample, we have identified the dominant source regions of atmospheric trace elements arriving at IORS. Aerosols are primarily affected by air masses from China from autumn to spring, which bring po