Aerosol residence times and changes in radioiodine-131I and radiocaesium-137Cs activity over Central Poland after the Fukushima-Daiichi nuclear reactor accident

Abstract

The first detectable activities of radioiodine ¹³¹I, and radiocaesium ¹³⁴Cs and ¹³⁷Cs in the air over Central Poland were measured in dust samples collected by the ASS-500 station in the period of 21^st to 24^th of March, 2011. However, the highest activity of both fission products, ¹³¹I and ¹³⁷Cs: 8.3 mBq m⁻³ and 0.75 mBq m⁻³, respectively, were obtained in the samples collected on 30^th March, i.e. ∼18 days after the beginning of the fission products’ discharge from the damaged units of the Fukushima Daiichi Nuclear Power Plant. The simultaneously determined corrected aerosol residence time for the same samples by ²¹⁰Pb/²¹⁰Bi and ²¹⁰Pb/²¹⁰Po methods was equal to 10 days. Additionally, on the basis of the activity ratio of two other natural cosmogenic radionuclides, ⁷Be and ²²Na in these aerosol samples, it was possible to estimate the aerosol residence time at ∼150 days for the solid particles coming from the stratospheric fallout. These data, as well as the differences in the activity size distribution of ⁷Be and ¹³¹I in the air particulate matter, show, in contrast to the Chernobyl discharge, a negligible input of stratospheric transport of Fukushima-released fission products.