Radon-222 in outdoor air in the Finnish arctic

Full text: The Finnish Meteorological Institute has been measuring airborne radon-222 at its air quality monitoring station at Sevettijaervi, Northern Finland (69 deg. 35'N, 28 deg. 50'E) since 1995. The 222Rn content of the air was monitored continuously by counting the beta particle emissions of the particle-bound daughter nuclides 214Pb and 214Bi collected onto glass-fibre filters. The observed 222Rn activity concentrations in the air were log normally distributed. The diurnal variation of the 222Rn concentrations was relatively large in August and September due to simultaneous strong radon exhalation and frequent nocturnal surface inversions. The lowest concentrations were measured in May, when the snow cover hinders the exhalation of radon and the almost continuous solar radiation causes efficient vertical mixing of the lower troposphere. In winter, during the polar night, the 222Rn concentrations are high because of the stagnant conditions of the surface air. To identify the source areas of 222Rn the observed afternoon concentrations were connected to concurrent air mass back trajectories calculated with the computer code TRADOS. As expected, the highest 222Rn concentrations were found in air masses coming from north-west Russia and the lowest concentrations in air masses coming from the Barents and Norwegian Seas. However, unanticipatedly high concentrations were found in air masses from the area between the 70th and 80th latitude over or near Greenland indicating a slight contribution from North America. A comparison to observed atmospheric sulphur dioxide concentrations indicates that the mining and metallurgical industry at Kola peninsula does not cause any technologically enhanced 222Rn concentrations in Northern Finland. (author)