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.