/sup 210/Pb and /sup 137/Cs in air and soils measure the rate and vertical profile of aerosol scavenging

We have determined the deposition rates of /sup 210/Pb and /sup 137/Cs from the atmosphere to the landscape of the eastern and mid-western United States by measuring their inventories in core samples of undisturbed soils. The mean inventories in lowland sites are 27.7 dpm cm2 for /sup 210/Pb and 21.8 dpm cm-2 for /sup 137/Cs as of January, 1984. The mean annual concentration of /sup 210/Pb in surface air at the 9 sites of the SURE network decreases smoothly from about 0.060 dpm m-3 near the Mississippi River to about 0.030 near the Atlantic coast. The ratio of deposition rate to surface air concentration is 0.62 +- 0.03 cm s-1 for /sup 210/Pb and 1.36 +- 0.08 cm s-1 for /sup 137/Cs. Using the activity vs. altitude profiles of Moore, et al. [1973], for /sup 210/Pb and the fission product nuclide, /sup 90/Sr, we calculate tropospheric aerosol mean residence times for /sup 210/Pb and /sup 137/Cs, of 4.8 and 5.5 days, respectively. This near equality precludes a rapid decrease of the aerosol scavenging rate constant in the mid-troposphere. The /sup 137/Cs//sup 210/Pb ratios in soils from elevations above 1000 m in the Appalachian Mountains are lower than those in adjacent lowland soils, indicating the preferential removal of aerosols from the lower layer of the troposphere, presumably by cloud droplet impaction or by seeder-feeder clouds