Multi isotope systematics of precipitation to trace the sources of air pollutants in Seoul, Korea

Multiple sulfur (δ34Ssulfate, Δ33Ssulfate, & Δ36Ssulfate), nitrogen and oxygen (δ15Nnitrate & δ18Onitrate) and strontium (87Sr/86Sr) isotope compositions of precipitation collected from Seoul, South Korea were analyzed to study the sources, transportation and deposition of air pollutants in East Asia region. The δ34Ssulfate values (from 1.9 to 14.6 ‰ with an average of 5.2 ± 2.7 ‰) and the δ15Nnitrate values (from -2.0 to 13.3 ‰ with an average of 1.9 ± 3.0 ‰) suggest that fossil fuel use (emission from coal combustion and vehicle exhaust) is predominant source for sulfur and nitrogen, but other natural sources including biogenic activities, DMS and lightning also contribute to their total budget. The seasonal variations are observed in δ34Ssulfate and δ15Nnitrate values (both higher in winter season), which is likely to result from the increase of coal for domestic heating in China. The δ18Onitrate values also varied seasonally depending on the NOx oxidation pathway, causing about 20 ‰ higher in winter season than summer season. Non anomalous Δ33Ssulfate and Δ36Ssulfate values show the absence of MIF signals in precipitation of Seoul. The 87Sr/86Sr ratio of the precipitation samples range from 0.7099 to 0.7149 with an average of 0.7111 ± 0.0004, indicating the influence of at least three end-member (silicate dust, carbonate dust and anthropogenic emission). Ionic ratios such as (K++NH4+)/(Ca2++Mg2+) and Cl-/Na+ suggest the overwhelming effect of anthropogenic input rather than carbonate dust on lower 87Sr/86Sr ratios end-member.