Sulfur isotope and chemical compositions of the wet precipitation in two major urban areas, Seoul and Busan, Korea

• The δ34S values in wet precipitation in the cities, Seoul and Busan, Korea.
• The δ34S values in the Seoul may be affected by anthropogenic sulfur dioxide.
• The δ34S values of Busan may be influenced by seawater spray.
• S isotopes as a tracer for atmospheric pollution studies.

The seasonal variations of δ34S together with major ions in snow and rainwater samples were measured in urban areas. Precipitation samples were collected from metropolitan city, Seoul and large port city, Busan, Korea, for about one year from June 2002 to June 2003. The δ34S values of sulfate in precipitation ranged from −4.3‰ to +6.6‰ (mean: 3.72‰) and +1.0‰ to +18.6‰ (mean: 5.55‰) in Seoul and Busan, respectively. Even though both of the study areas have large populations and transportation infrastructure, δ34S values of sulfate in Seoul precipitation originate more from anthropogenic sources relative to that of Busan. The elevated anthropogenic sources in Seoul might be influenced by human activities from surrounding industrial cities, while the scatter of δ34S values in Busan may be influenced by marine air. During the study, δ34S values are high in the fall season and low in the spring season. It may be inferred from this data that spring time δ34S values are affected more by biogenic sources compared to the fall season. As such, Seoul and Busan showed significant differences in chemical compositions, such as δ34S and nss-SO42-. Especially, δ34S values in the Seoul show very good relationship with anthropogenic emissions (e.g., emission from coal combustion) and δ34S values in the Busan may be influenced by sea spray from the oceanic surface micro-layer. This correlation and the δ34S values indicate that the major source in this region is likely to be anthropogenic source in Seoul and sea spray in Busan, rather than traditionally suggested sources such as soil resuspension, stratospheric air intrusion, volcanic emissions, and biogenic emissions.