TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 44 (No. 6), pp. 571-577, 2010


Ten-year observation of sulfur isotopic composition of sulfate in aerosols collected at Tsuruoka, a coastal area on the Sea of Japan in northern Japan

Naofumi Akata,1 Fumitaka Yanagisawa,1 Takashi Kotani2 and Akira Ueda3

1Graduate School of Science and Engineering, Yamagata University, Yamagata 990-8560, Japan
2Tsuruoka National College of Technology, Tsuruoka, Yamagata 997-8511, Japan
3Graduate School of Engineering, Kyoto University, Kyoto 615-8540, Japan

(Received June 25, 2009; Accepted June 4, 2010)

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 samSO42- and nssSO42- 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 samSO42- and nssSO42- 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.
Key words: long-term observation, aerosol, sulfate, δ34S

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