Measurement of 210Pb, 210Po, and 210Bi, in size-fractionated atmospheric aerosols: an estimate of fine-aerosol residence times

Lead-210 and 210Po were measured in size-fractionated aerosol samples collected at several sites in North America. Total particulate mass concentrations of the samples were 23-98 μg/m3, with 23-67% of the mass in size ranges below 2 μm. The aerosol mass size distributions below 9 μm were generally bimodal, with a maximum in the coarse-particle range occurring primarily at 3.1 μm and a maximum in the accumulation range occurring at approximately 0.6 μm. Total 210Pb concentrations were 0.51-1.7 mBq/m3, with 63-97% occurring in the size ranges below 2 μm. The 210Po/210Pb ratios suggested residence times of 33-66 days for the aerosols below 2 μm. The 210Bi/210Pb ratios of selected samples gave similar results to the 210Po/210Pb ratios, leading to residence times of 6-67 days, with the largest differences occurring in the larger size ranges