222Rn and 210Pb in the Arctic summer air

As part of an extensive air chemistry programme, during summer 1980, on board the Swedish ice-breaker 'Ymer', levels of 222Rn, 210Pb and 210Po were measured. The radon was trapped on charcoal and the long-lived daughter products sampled daily on filters. In addition, short-lived progenies were followed continuously on the filters to achieve a time resolution of about one hour. The concentrations of radon and 210Pb in the Arctic summer air north of latitude 750 N averaged 75+-21 and 0.075+-0.028 mBq m-3, respectively. During a two week period of persistent polar winds, the mean radon concentration was 19+-5 mBq m-3. During such 'Arctic background' conditions, radon exhalation from the sea may contribute significantly to the measured radon-in-air concentration. Steady-state equilibrium models, applied to an air mass over the sea, overestimate the aerosol residence-time calculated from activity ratios. Time-dependent calculations indicate a mean aerosol residence time of 4 to 7 d in Arctic air. Good agreement is observed between radon levels and the time since the air mass left larger land areas. both the 222Rn and the long-lived daughter measurements are insensitive to contamination from ship and local settlements. (author)