Annual distribution and atmospheric deposition of 210Po and 210Pb in aerosols in Busan, the largest port city in Korea

The annual distributions of radionuclides, 210Po and 210Pb, were investigated in Busan, South Korea, whose regional atmosphere is largely affected by port infrastructure. Aerosol samples were collected from Apr. 2019 to Feb. 2020 using a high-volume air sampler. The activities of 210Po and 210Pb ranged from 0.01 - 0.40 mBq m-3 (average=0.13±0.2 (1 σ) mBq m-3, n=90) and 0.10 - 1.7 mBq m-3 (average=0.65±0.9 (1 σ) mBq m-3 n=91), respectively. In contrast to 210Pb activity, which was relatively consistent in the entire sampling period, 210Po activity showed a variation of up to 3 factors and was remarkably higher in the autumn and winter (Sep. to Feb.) relative to summer activity (Jun. to Aug.). The substantially higher 210Po activity during the autumn and winter seasons was attributable to anthropogenic input from the vast port area surrounded by maritime infrastructures (e.g., shipyard, trade warehouse, factories, and ship anchorage), together with seasonal changes in wind directions. In Busan, the levels of 210Po and its dry depositional fluxes were comparable or slightly higher (1 - 2 times) than those in other regions worldwide. We also attempted to quantify the aerosol residence time based on a 210Po-210Pb tracer, which suggested the mean aerosol residence time in Busan to be 41 to 48 days. These results imply that aerosols that exist in harbor cities can interact with and affect individuals and the surrounding society, where the influence is likely to last for weeks to months.