Lead isotope ratio in rainfall collected by a sequential sampler in central Tokyo

Rainfall at central Tokyo was sequentially collected with a 1-mm precipitation interval. Lead (Pb) concentrations and isotopic compositions of each fraction were precisely determined by an inductively coupled plasma-quadrupole mass spectrometry and a multiple collector-inductively coupled plasma-mass spectrometry, respectively. The results showed that (1) Pb concentration in rainfall decayed according to a power law function along with rainfall depth; (2) Pb isotope ratios clearly changed during a single rainfall event; (3) mixing model having four or more end members could explain the variations of Pb isotope ratio; (4) Pb in rainfall was probably affected by diesel vehicle emission control commenced on 1st October 2003. Concerning (3), candidates of end member were estimated as local materials, e.g., natural soil components, airborne particle matter, automobile exhaust gases and fly ash from a municipal incinerator. (author)