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28,890,000 Yen (FY1998; 9,495,000 Yen)
About 200 leaf samples of Cryptomeria japonica D. Don (and some other conifers) were collected from various areas in Japan (urban, suburban and rural areas, remote island, etc.). Aerosols deposited on the leaves were separated by dissolving the epicuticular wax with chloroform, and collected on quartz wool. They were then analysed for 29 elements by neutron activation analysis. Deposition of aerosols on the leaves began just after leaf expansion (in May or June), and its amount increased with time to reach a maximum and steady level in winter. The amounts of aerosols per unit leaf weight (or area) were larger in conifers than in broad-leaved trees. Although elements in the aerosols had various origins (fossil fuels, sea-salts, volcanic gases and soils), more than 90% of Au, Ag, Sb, Cl, Se and I, 80-90% of Br, Zn and As, 40-60% of Cr, Cs, Co and V, and ca. 30% of Fe and Na were non-soil fractions, whereas Th, Hf, Rb, Ta, Ti, Mn, Al and rare earth elements originated mostly from soils. Sb, which originated mainly from combustion of fossil fuels, was highly enriched in the aerosols (enrichment factor vs. soils: >100), in spite of its low natural abundance. Since Sb accumulates on leaves and subsequently in surface soil due to washing-down, it is a good indicator for evaluating the load of atmospheric pollutants in soil and vegetation. For instance, the amount of Sb deposited on 1-year leaves of C. japonica reached more than 100 ng/g-fresh leaves in heavily polluted areas of Saitama Prefecture (cf. ca. 10 ng/g-fresh leaves on Yakushima Island, Kagoshima). Since the origin of Sb and the mechanism of its atmospheric transport are expected to be similar to those of S and N compounds, the load of acidic pollutants may be estimated from the amount of Sb that accumulates in the environment.
Aerosol, Dry-deposition, Japanese cedar (Cryptomeria japonica), Sb, Neutron activation analysis