Aerosol residence times and iodine gas/particle conversion over the North Pacific as determined from Chernobyl radioactivity

抄録

Radioactivity from the Chernobyl accident present on aerosols was measured at several island sites and on a ship in the North Pacific. The radioactivity arrived at the various sites located from 11°-64°N between 6-14 May 1986. Isentropic trajectory analyses and measurement of the natural radioactive species ⁷Be and ²²²Rn indicate that the continental air containing Chernobyl fission products (e.g., ¹³¹I, ¹³⁷Cs) was transported to the central North Pacific through the middle troposphere. We estimate the residence time and gas-to-particle conversion times by combining the radionuclide data with surface concentration estimates in Japan. The atmospheric residence time over the North Pacific for the aerosols containing the fission products was 3-5 days. The calculated mean gas-to-particle conversion time for radioactive ¹³¹I was 2-3 weeks, with a minimum of ∼12 days. The results indicate that the radioactive submicrometer aerosol and the iodine gas from the Chernobyl explosion have residence and conversion times similar to those of naturally occurring aerosols and gases in the atmosphere.