Three-year determination of trace metals and the lead isotope ratio in rain and snow depositions collected in Higashi-Hiroshima, Japan

The concentrations of 14 elements (Al, Ba, Ca, Cd, Cu, K, Mg, Mn, Na, Ni, P b, Sr, V and Zn) and five ions (Cl-,NO3-, SO42-, NH4+ and H+) in wet deposi tions are reported. Samples were collected in Higashi-Hiroshima in western Japan for 3 years (1995-1997). The characteristic variations of these speci es were investigated in terms of the source of atmospheric heavy metals. Th e elements were classified into three categories by principal component ana lysis; constituents from an anthropogenic source (Cd, Cu, Pb, V, Zn, NO3-, SO42-, NH4+ and H+), elements associated with crustal source (Al, Ba, Ca, a nd Mn) and elements from sea salts (Na, Mg and Cl-). The depositions and co ncentrations of the elements associated with soil dust were peculiarly enha nced in the spring. The Kosa phenomenon, in which yellow soil dust was tran sported From Asian deserts by strong westerly winds in spring, is a possibl e reason of increased deposition and concentration of the elements. Soil-de rived elements were washed out at the early stage of a precipitation event, and their concentrations were mostly controlled by dilution. For the anthr opogenic elements, such as Cd, Pb and Zn, no systematic seasonal variation in wet deposition was observed. Log-log plots of precipitation volume and t he concentration of anthropogenic elements suggested that the concentration s of these elements were controlled not only by dilution but also by other factors. Lead isotope ratios changed in winter. The changes must be associa ted with pollutant-enriched aerosols and snow particles transported from th e Asian continent by strong northwest monsoons, since lead isotope ratios i n aerosols transported from Asian continent are different from those in Jap anese aerosol. The chemical species in snow depositions collected between t he Sea of Japan and the Seto Inland Sea were also determined to evaluate th e long-range transport of pollutants from the Asian continent in winter. (C ) 2000 Elsevier Science Ltd. All rights reserved.