Sulfur and oxygen isotopic compositions of the dissolved sulphate in the meteoric water in Chuncheon, Korea

초록

The meteoric water deposited in the Chuncheon area was collected from July 2002 to May 2004 and its chemical and isotopic compositions were analyzed to examine if the isotopic data can help trace the sources of the sulfur pollutant and understand the details of acid formation processes in the air. The chemical compositions of the meteoric water indicate that the sulfate mostly comes from anthropogenic sources. The sulfur isotopic compositions of the dissolved sulfate in the meteoric water (delta S-34(S04)) vary from 2.6 to 7.5 parts per thousand with little seasonal differences, which are significantly different from those of the sulfur in the coal being locally consumed (-4.5 to -0.7 parts per thousand). This difference indicates that the local coal consumption gives insignificant contribution to the pollutant sulfur in the acid deposition of the area. The relationship between delta S-34(S04) and the concentration of sulfate suggests that the sources of pollutant sulfur are variable and inhomogeneous. The oxygen isotopic compositions of the dissolved sulfate in the meteoric water delta O-18(S04)) range from 9.0 to 17.2 parts per thousand, which are generally lower in winter than in spring. Comparison between the measured and calculated values of delta O-18(S04) suggests that the oxygen isotopic exchange between sulfite and water occurs before its oxidation to sulfate. The extent of isotopic exchange seems to be not controlled by equilibrium but by kinetic fractionation. The poor correlation between delta O-18(S04) and the oxygen isotopic composition of the meteoric water confirms the disequilibrium nature of the isotopic exchange.

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