Sulfur, oxygen, and hydrogen isotope compositions of precipitation in Seoul, South Korea

To evaluate the source of sulfur and the extent of seasonal and local characteristics in Seoul's precipitation chemistry, we measured sulfur, oxyeen, and hydrogen isotopic ratios of precipitation. The pH of precipitation ranges from 4.6 to 7.0 in Seoul. Precipitation shows positive correlations between ions in the Ca2+-Mg2+-SO42--NO3- system, indicating that the dissolution of Ca and Ma particles by H2SO4 and HNO3 from the combustion of fossil fuels is a major process controlling the chemical composition of snow and rain. The values of oxygen and hydrogen isotope composition of rain range -15.7 similar to-3.2 parts per thousand and -114.7 similar to-18.0 parts per thousand, respectively. The H and 0 isotope values in the summer are plotted near the global meteoric water line by Craig (1961). The d-excess values in winter are higher than 10, which indicate that the source of rain during winter is a dry air mass from continental China. The sulfur isotope ratio of precipitation in Seoul ranges from +3.0 to +7.3 parts per thousand, which is similar to typical metropolitan air pollution levels. The data suggests that the main source of sulfur is SO2 produced by the combustion of fossil fuels. The pollutant SO4 is estimated to have a delta S-34(nss) ss range from +1.0 to +6.2 parts per thousand in the Seoul area. The delta S-34 values of precipitation range from +5.1 to +7.3 parts per thousand (mean +6.4 parts per thousand) in winter and from +3.0 to 4.8 parts per thousand (mean +4.0 parts per thousand) in summer. The higher delta S-34 values in winter (December and February) seem to be correlated to the air mass from northern China, of which the delta S-34 values of oil or coal is higher than that of southern China. The lower sulfur isotopic values in summer (June to August) are correlated to the air mass moving from southern China. Isotopic composition and chemical concentrations of SO4 depend on wind provenance, thus supporting the idea that a seasonally transported source for the pollutant sulfur is from China.