Radon-222 on the island of Hawaii

The island of Hawaii, like other locations in a marine environment, has low levels of atmospheric 222Rn. The low concentrations of 222Rn and its decay products result from a low average flux density of 9.8 mBq m-2 s-1, the mixing of marine air from the Pacific having a 222Rn concentration of only 0.04 Bq m-3 with air from over the island, and the decay of 222Rn as it is transported in air masses across the Pacific primarily from the Asian continent. The overall mean concentration over the Island The overall mean concentration over the Island was found to be 0.44 Bq m-3 compared with a figure of about 8 Bq m-3 for air over continents. A consideration of the island as a source of 222Rn must take into account the relatively low average flux density associated with the lava fields and accompanying thin soils. The 222Rn formed from the U and 226Ra present in the lava cannot escape to the atmosphere. The deep agricultural soils, on the other hand, provide relatively high flux densities. When the areas of the soil types are taken into account, the exhalation for the lava fields, thin organic soils, and deep agricultural soils were 0.25, 1.7, and 32 MBq s-1, respectively. Measurements of indoor 222Rn on the island indicate levels of approximately 25 Bq m-3 which is appreciably lower than 40 Bq m-3 taken as an average for indoor levels on the mainland. Based on an assumed indoor occupancy level of 0.8, the effective dose equivalent for inhaled 222Rn and its decay products on Hawaii is 1.2 mSv y-1. This is only a little more than one-half of that for a resident of the continental United States who is estimated to receive an effective dose equivalent of 2 mSv y-1. The relatively low effective dose equivalent for the population on the island may have interesting effects in comparison with people living in areas where the inhaled dose from 222Rn is much higher.