The origin and migration of the dissolved sulfate from precipitation in Seoul, Korea

This study incorporated stable isotope analyses with chemical analyses to determine the origin and migration of sulfur sources in East Asia, and these findings were compared with our decadal research from 2000 to 2001 and 2002 to 2003. The multiple sulfur isotope composition (³²S, ³³S and ³⁴S) of the dissolved sulfate in precipitation was first measured from 2011 to 2013 in Seoul, South Korea. The δ³⁴S_nss values were -1.1‰ to 7.9‰ (avg. 3.6‰), strongly suggesting that sulfur derived from the combustion of Chinese coal is the predominant source of sulfate in the Seoul region. Low NO₃/SO₄^2- ratios in the precipitation samples indicated an insignificant effect of sulfur from vehicle exhaust. The seasonal variation of δ³⁴S_nss values appears to be caused by increasing biogenic sulfur activity during the spring and summer seasons. The some Δ³³S values (0.13‰-0.16‰) measured in the three samples were sufficiently small; thus, whether these values can be attributed to mass-independent fractionation remains unclear. Measuring the Δ³³S anomalies in dissolved sulfate provides valuable insights for identifying the sources of sulfur transferred from the stratosphere to the troposphere and upper troposphere.