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

Lead-210 and {sup 210}Po were measured in size-fractionated aerosol samples collected at several sites in North America. Total particulate mass concentrations of the samples were 23-98 {mu}g/m{sup 3}, with 23-67% of the mass in size ranges below 2 {mu}m. The aerosol mass size distributions below 9 {mu}m were generally bimodal, with a maximum in the coarse-particle range occurring primarily at 3.1 {mu}m and a maximum in the accumulation range occurring at approximately 0.6 {mu}m. Total {sup 210}Pb concentrations were 0.51-1.7 mBq/m{sup 3}, with 63-97% occurring in the size ranges below 2 {mu}m. The {sup 210}Po/{sup 210}Pb ratios suggested residence times of 33-66 days for the aerosols below 2 {mu}m. The {sup 210}Bi/{sup 210}Pb ratios of selected samples gave similar results to the {sup 210}Po/{sup 210}Pb ratios, leading to residence times of 6-67 days, with the largest differences occurring in the larger size ranges.