Lead and sulfur isotopic ratios in precipitation and their relations to trans-boundary atmospheric pollution

Abstract

We measured the lead (Pb) and sulfur (S) isotopic ratios in precipitation collected in Toyama Prefecture, Japan, to investigate their characteristics as tracers for trans-boundary air pollution. The Pb concentrations and isotopic ratios were measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). A relatively higher 207Pb/206Pb isotopic ratio (area 3: Northern China, 0.869±0.003; area 4: Central China and Korea, 0.870±0.006) was assumed to be related to Northern Asian sources, whereas the samples influenced by Japanese air mass showed a lower 207Pb/206Pb ratio (area 5: Japan, 0.863±0.004). Sulfur ion was measured by Ion Chromatography (IC), and S isotopic ratios were measured by Mass Spectrometry. The S isotopic ratios' weighted average values (area 3: 4.9±1.4‰; area 4: 6.3±1.5‰) of the Asian continent showed a higher isotopic ratio than that of Japan (area 5: 3.6±1.8‰). It was difficult to use the NO3−/non-sea-salt SO42− (nss SO42−) (N/S) ratio's weighted average values to distinguish the Japanese origin (area 5: 0.71) from the continental origin (area 3: 0.68, area 4: 0.66). We attempted to use the S isotopic ratio in addition to the lead isotopic ratio to characterize the transported East Asian air pollution, and as a result we found that the combination of these isotopic ratios was useful for identifying the origin of air pollution in the East Asian region.