ION-INDUCED NUCLEATION AROUND RADON DAUGHTERS IN REMOTE ARCTIC MARITIME AIR

Measurements made of radon daughters during the International Arctic O cean Expedition of 1991 did not usually show the expected decrease in apparent concentration due to losses to the surface when aerosol conce ntrations were very low. The evidence suggests that except on some occ asions after the equinox when the air had been near the North Pole for the previous 5 days, sufficient supersaturations of condensible vapou rs existed to allow nucleation of new particles on radioactively produ ced ions. This would drastically reduce the mobility of the ions and t herefore surface losses. As a result, the measurement usually gave a s atisfactory estimate of radon that was very useful in checking on air trajectory predictions and providing more detailed information on cont act of the air with land. The exceptions suggest that the measurement might be quite unreliable in conditions where aerosol and oxidizable g as concentrations are very low such as in the Arctic or Antarctic wint er.