ABSTRACT

Atmospheric aerosol samples were collected from 1993 to 2003 at Tsuruoka, Japan, a coastal area on the Sea of Japan. Concentration of water-soluble chemical components and sulfur isotopic ratios of sulfate in aerosol samples were measured to evaluate the temporal variation and identify the source. The _samSO₄^2- and _nssSO₄^2- concentrations range from 7.6 to 354.4 and 3.7 to 335.6 neq m^-3, respectively, and there was no clear seasonal variation. Sulfur isotope ratios of total sulfate (_samδ³⁴S) and non-sea salt sulfate (_nssδ³⁴S) in aerosols are +1.0 to +15.1 with a mean value of +5.7‰ and -4.4 to +14.5 with a mean value of +4.1‰, respectively. The values of _samδ³⁴S and _nssδ³⁴S are relatively low in summer and high in the other three seasons. The _nssδ³⁴S values of aerosols in fall to spring agree with the average sulfur isotope ratios of coal used in northern China, considering the isotope fractionation. These results indicate the possibility of long-range transport of sulfate from the Asian continent to Japan. The variations of atmospheric _samSO₄^2- and _nssSO₄^2- concentrations decreased gradually and reach a minimum in 1999. The decline of SO₂ emission in China due to reduction in industrial coal use, a slowdown of the Chinese economy, and the closure of small and inefficient plants would be among the causes of this decreasing observed trend. On the other hands, the variation ranges of _samδ³⁴S and _nssδ³⁴S values abruptly changed after 2000. The introduction of fuel-gas desulfurization technologies to industrial plants of coke production and thermal power stations would be one of the most important causes of this change.