Radionuclides from the Fukushima accident in the air over Lithuania: measurement and modelling approaches

Analyses of 131I, 137Cs and 134Cs in airborne aerosols were carried out in daily samples in Vilnius, Lithuania after the Fukushima accident during the period of March–April, 2011. The activity concentrations of 131I and 137Cs ranged from 12 μBq/m3 and 1.4 μBq/m3 to 3700 μBq/m3 and 1040 μBq/m3, respectively. The activity concentration of 239,240Pu in one aerosol sample collected from 23 March to 15 April, 2011 was found to be 44.5 nBq/m3. The two maxima found in radionuclide concentrations were related to complicated long-range air mass transport from Japan across the Pacific, the North America and the Atlantic Ocean to Central Europe as indicated by modelling. HYSPLIT backward trajectories and meteorological data were applied for interpretation of activity variations of measured radionuclides observed at the site of investigation. 7Be and 212Pb activity concentrations and their ratios were used as tracers of vertical transport of air masses. Fukushima data were compared with the data obtained during the Chernobyl accident and in the post Chernobyl period. The activity concentrations of 131I and 137Cs were found to be by 4 orders of magnitude lower as compared to the Chernobyl accident. The activity ratio of 134Cs/137Cs was around 1 with small variations only. The activity ratio of 238Pu/239,240Pu in the aerosol sample was 1.2, indicating a presence of the spent fuel of different origin than that of the Chernobyl accident.

► Two observed maxima in radionuclide concentrations were related to air mass transport.
► HYSPLIT backward trajectories were applied for data interpretation.
► 7Be and 212Pb were used to study a vertical transport of air masses.
► The 134Cs/137Cs activity ratio was around 1.
► 238Pu/239,240Pu ratio was different from global fallout and Chernobyl accident.