Measurements of the levels of Be-7 and Pb-210 are reported for rain, s
now, and hail samples taken at Argonne, Illinois, and Socorro, New Mex
ico. These natural radioisotopes are indicators of the sources of the
aerosols contributing materials to the precipitation samples. The data
presented indicate that the more soluble Be-7 is enriched in the prec
ipitation samples with respect to Pb-210, as compared to the ratios of
these radioisotopes found in aerosol samples. Use of the Pb-210/Pb-21
0 activity ratios as an internal clock indicated that the aerosols con
tributing to the precipitation ranged in age from 10 to 47 days. Level
s of Be-7 ranged from 11 to 55 pCi L-1 for the samples, with the highe
st levels in a stratus precipitation event and in a thunderstorm with
the lowest wet deposition rate. These results are discussed with regar
d to the potential for use of these radioisotopes in the determination
of stratospheric-tropospheric mixing and in their geochemical usage a
s indicators of sedimentation rates.