We have measured the concentrations of 210Po, 210Pb, SO4(2-), Na+, and 34S in precipitation samples from two metropolitan cities, Seoul and Busan, Korea. The delta34S values ranged from 0 to 10% in most Seoul and Busan precipitation samples, indicating major contributions from industrial sources to S levels. A high level of excess 210Po, which is not produced by 210Pb decay in the troposphere, was observed in both regions. The excess 210Po 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 delta34S values. In Seoul precipitations, we observed a good correlation between non-sea-salt SO4(2-) and excess 210Po, suggesting that both species are controlled mainly by the same factor. This correlation and the delta34S 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.