Trans-boundary air pollution in East Asia is a serious problem, and several studies indicated sulfate (SO₄^2-) have been transported from Asian continent to the areas along the Japan Sea (JS). In this study, the amounts of SO₄^2- and stable isotope ratio of sulfur (δ³⁴S) in 35 forest soils (25 sites from the areas along JS and control 10 sites from inland areas) were measured to know distributions and accumulation of SO₄^2-, and to discuss its source. SO₄^2- in soil sample was extracted with 500ppmP Ca(H₂PO₄)₂ solutions and the concentrations were determined by IC. δ³⁴S was analyzed by MS using the δ-notation with respect to the SO₂-based V-CDT standard.

Mean of the amount of SO₄^2- as weighted average with the depth of soil from the areas along JS was 7.4mmol kg^-1, which was significantly higher than that of inland areas (3.2mmol kg^-1). The values of δ³⁴S of the areas along JS ranged from 8.6 to 17.3‰ (mean: 12.9‰). Recalculated δ³⁴S value of non-sea salt SO₄^2- after the elimination of sea salt contribution in these areas (annual mean 40%; MOE, 2009) was about 8.0‰, and it approximated the δ³⁴S values of the coal used in China (7.8±11.0‰; Maruyama et al., 2000). While δ³⁴S values of inland areas ranged from 2.51 to 7.16‰. The sources of these lighter values were probably from the mixing of SO₄^2- from oil used in Japan and volcanic activities.