Radon at the Mauna Loa observatory: Transport from distant continents

Continuous measurements of radon have been made at an altitude of 3400 m at the Mauna Loa Observatory, Hawaii. Concentrations ranged from about 20 to more than 700 mBq m⁻³. These were similar to values at remote Macquarie I., some 2000 km south of Australia in the Southern Ocean. At Mauna Loa, the radon concentrations could usually be separated into free tropospheric and island influenced categories on the basis of local meteorological observations. On one occasion a long range transport event from Asia brought relatively high radon concentrations to Mauna Loa and persisted for several days. The Asian origin of this event was supported by wind trajectories. This measurement program demonstrates the value of radon data in evaluating air transport models and the influence of transport from distant continents on baseline atmospheric measurements.