Source and Pathway of ¹³¹I, ¹³⁴Cs and ¹³⁷Cs in Aerosols of Shanghai After the Fukushima Nuclear Accident

The typical radionuclides (¹³¹I and ^{134, 137}Cs) in aerosols could be efficiently used to evaluate the impacts of radioactive materials from the Fukushima nuclear accident on the radioactive background level of the atmosphere in Shanghai and the world. In the present work, combining impact factors, such as the nuclear accident release process, natural radioactive decay and the meteorological conditions, the distribution patterns of ¹³¹I and ^{134, 137}Cs activities and their ratios in Shanghai aerosols were obtained. The date when ¹³¹I (2011-03-27) could be detectable is earlier than ¹³⁴Cs (2011-04-06) and ¹³⁷Cs (2011-04-08). The ¹³¹I activity  (0.01-1.20 mBq/m³) is 2-10 times higher than those of ¹³⁴Cs (0.01-0.58 mBq/m³) and ¹³⁷Cs (0.01-0.65 mBq/m³). Moreover, multiple peak values of ¹³¹I are found with time series. The activity ratios of ¹³¹I/¹³⁷Cs (1.3-10.6) decrease after the date of April 5^th, 2011, however, the activity ratios of ¹³⁴Cs/¹³⁷Cs (0.8-2.9) are constant to be around 1.1. Using the analytical method of HYSPLIT model, the primary air mass migration pathways of radio-aerosols in Shanghai during this accident can be qualitatively inferred as the northeast and northwest paths. Meanwhile, the northeast pathway of radio-aerosols in Shanghai is further confirmed to be dominant by analysis of the reported radio-aerosol data in the concerned cities of China during that time period. In addition, the results of maximum values of ¹³¹I/¹³⁷Cs and ¹³⁴Cs/¹³⁷Cs activity ratios are summarized and analyzed to reveal the spreading pathways of radio-aerosols in the northern hemisphere.