Measurement of Pb-210, Po-210, and Bi-210 in size-fractionated atmosphericaerosols: An estimate of fine-aerosol residence times

Lead-210 and Po-210 were measured in size-fractionated aerosol samples coll ected at several sites in North America. Total particulate mass concentrati ons of the samples were 23-98 mu g/m(3), with 23-67% of the mass in size ra nges below 2 mu m. The aerosol mass size distributions below 9 mu m were ge nerally bimodal, with a maximum in the coarse-particle range occurring prim arily at 3.1 mu m and a maximum in the accumulation range occurring at appr oximately 0.6 mu m. Total Pb-210 concentrations were 0.51-1.7 mBq/m(3), wit h 63-97% occurring in the size ranges below 2 mu m. The Po-210/Pb-210 ratio s suggested residence times of 33-66 days for the aerosols below 2 mu m. Th e Bi-210/Pb-210 ratios of selected samples gave similar results to the Po-2 10/Pb-210 ratios, leading to residence times of 6-67 days, with the largest differences occurring in the larger size ranges.