Lead isotopes in rainfall collected by a sequential sampler in suburban Tokyo |
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| Institution: | 1. Department of Environmental Science and Engineering, Xi''an Jiaotong University, Xi''an, China;2. Key Lab of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi''an, China;3. Institute of Global Environmental Change, Xi''an Jiaotong University, Xi''an, China;4. Desert Research Institute, Reno, USA;5. Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), Switzerland;6. School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China;1. Department of Subsurface Geobiological Analysis and Research, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan;2. Laboratory of Ocean-Earth Life Evolution Research (OELE), Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan;3. Submarine Hydrothermal System Research Group, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan;4. Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Tokyo, Japan;5. Department of Systems Innovation, School of Engineering, University of Tokyo, Tokyo, Japan;6. Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA;7. Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA |
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| Abstract: | Sequential rainfall collections were obtained with a 1-mm precipitation interval at a suburban site in Tokyo. The lead–isotope composition of each fraction was precisely determined by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The results showed that lead isotopes clearly changed during a single rainfall event for all rainfall events investigated, and large variations were observed for three specific events. In these three events, the values of the lead isotopes in the initial stage of rainfall (wash-out stage) were similar to the so-called common lead. As precipitation proceeded, the lead isotopes tended to be more radiogenic, and in the later stage (rain-out stage) they were highly radiogenic (up to 206, 207, 208Pb/204Pb=29.26, 26.03, and 63.64, respectively). The source of lead in the rain-out stage completely differed from that in the wash-out stage for these events. A simple mixing model with two end members (rain-out lead and wash-out lead) could explain the isotopic variations. Preliminary trajectory analysis indicated that the highly radiogenic lead was emitted and transported from South-West China. Coal combustion could be a candidate for rain-out stage lead by a selective emission of radiogenic isotopes (206Pb, 207Pb, 208Pb). A selective emission mechanism is discussed. The origin of the wash-out lead may have been local and derived from a mixture of urban particulates, e.g., particles from automobile exhaust, city incinerators, roadside dust, and factory exhaust. |
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