Stable isotope ratio of atmospheric and seawater nitrate in the East Sea in the northwestern Pacific ocean

The nitrogen and oxygen isotopic values of anthropogenic NO_x⁻ (including NO₂⁻ and NO₃⁻) are preserved in precipitation and airborne total suspended particles. Hence, isotope analyses of these atmospheric samples allow for the identification of the NO_x⁻ sources. In this study, atmospheric δ¹⁵N- and δ¹⁸O-NO_x⁻ values were measured in an eastern coastal site of South Korea over a three-year period, and compared with seawater values observed from coastal waters of the East Sea. The highest seasonal atmospheric δ¹⁵N-NO_x⁻ values were associated with wintertime air masses blowing from northeastern China, and similar to those produced by coal and biomass burning. By contrast, the lowest atmospheric δ¹⁵N-NO_x⁻ values were observed in summer, and the major source appeared to be vehicle exhaust. In addition, the reductions in the seawater δ¹⁵N-NO_x⁻ and Δ(15−18) (i.e., δ¹⁵N-NO_x⁻ minus δ¹⁸O-NO_x⁻) values in the East Sea could be at least partially attributed to atmospheric deposition.