Evidence for anthropogenic 210Po in the urban atmosphere of Seoul, Korea

We have measured the concentrations of Po-210, Pb-210, SO42- , Na+, and S-34 in ecipitation samples from two metropolitan cities, Seoul and Busan, Korea. The delta 34S values ranged from 0 to 10 parts per thousand in most Seoul and Busan precipitation samples, indicating major contributions from industrial sources to S levels. A high level of excess Po-210, which is not produced by Pb-210 decay in the troposphere, was observed in both regions. The excess Po-210 activities in some samples from Busan, a harbor city, were influenced strongly by sea salt (i.e., sea-surface microlayer) which could be traced using [Na+] and delta 34S values. In Seoul precipitations, we observed a good correlation between non sea-salt SO42- and excess Po-210, suggesting that both species are controlled mainly by the same factor, This correlation and the delta 34S values indicate that the major source for both species in this region is likely to be anthropogenic, rather than from traditionally suggested sources such as soil resuspension, stratospheric air intrusion, sea sprays, volcanic emissions, and biogenic emissions.