Abstract
A monitoring network of atmospheric 222Rn concentration as a tracer for long-range transport in East Asia was established. Atmospheric 222Rn concentration at Beijing, which is located on China Continent was 10- 20Bq m-3, at Nagoya, which is located on edge of terrestrial area was 3- 10 Bq m-3 and at Hachijo-jima and Hateruma-jima, which are solitary islands in Pacific Ocean was 0.5- 3 Bq m-3, respectively. The atmospheric 222Rn concentration variations were different from sites. The 222Rn concentration was the lowest in the summer and the highest in the winter except Nagoya where the highest was observed in the autumn and the lowest in the spring. Diurnal variations were measured at Beijing and Nagoya. In contrast, diurnal variations were not measured but several-day-cycle variations were measured at Hachijo-jima and Hateruma-jima.
It was pointed out by this study that the several-day-cycle variations at Hachijo-jima were dependent on synoptic-scale atmospheric disturbance. 222Rn concentration increased rapidly after a cold front passed through Hachijo-jima. Backward trajectory analysis of the relationship between atmospheric 222Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that air mass transported from China and Siberia has high concentration 222Rn and air mass transported from Pacific Ocean has low concentration 222Rn. In winter, atmospheric 222Rn concentrations at Hachijo-jima is dependent on vertical transport pathway rather than horizontal transport pathway.
