Measurements of Al, Pb, 210Pb, and 210Po in precipitation and aerosol were used to estimate wet and dry components of the atmospheric flux at a semiremote site in northern Wisconsin. Wet deposition was primarily responsible for removing airborne Pb, 210Po, while dry deposition was also important for Al. Although Pb and 210Pb both exhibited a wet/total ratio of about 0.8, precipitation washout ratios for Pb and 210Pb suggested that 210Pb was washed from the atmosphere with greater efficiency than was Pb. This phenomenon was also illustrated by comparing the weighted mean annual specific activity in precipitation (976 pCi 210Pb mg-1 Pb) and in aerosol (476 pCi 210Pb mg-1 Pb) at this site between June 1979 and June 1980. By consideration of the apparent differential precipitation washout of Pb and 210Pb, a reasonable estimate of the atmospheric flux of Pb was obtained by using the mean Pb/210Pb ratio in aerosol and the 210Pb flux. The atmospheric flux to northern Wisconsin was estimated to be 0.8 μg cm-2 yr-1 for Pb and 0.70 pCi cm-2 yr-1 for 210Pb. |