Aerosol particle size distribution of atmospheric lead-210 in northern Finland.

Size-segregated aerosol samples were collected with a high-volume 6-stage cascade impactor at Sodankylä, Finland, 100 km north of the Arctic Circle. The 210Pb content of the samples were determined with radiochemical separation of in-grown 210Po followed by alpha spectrometry. Most of the 210Pb activity was incorporated in accumulation mode aerosol particles. The activity median aerodynamic diameter (AMAD) ranged from 0.53 μm to 0.98 μm 38-61 per cent of 210Pb activity was found to be associated with aerosol particles smaller than 0.69 μm. A slight downward tendency of 210Pb activity median aerodynamic diameter was observed as a function of increasing 210Pb activity concentration. This is related to the continental origin of airborne 210Pb on one hand, and various aerosol particle growth processes on the other hand. Also a clear tendency towards a higher 7Be/210Pb activity ratio as a function of increasing aerosol particle diameter was observed. This, in turn, reflects the different origin of 210Pb, exhalation of 222Rn from the soil into the air, and 7Be, formation by cosmic radiation in the upper troposphere and the stratosphere.