Atmospheric deposition of Pb and 210Pb

As part of a continuing program for evaluation of the performance of the Health and Safety Laboratory (HASL) wet/dry deposition collector, as well as for developing a data base of atmospherically deposited substances, measurements of Pb and 210Pb have been carried out on samples collected at the Chester site for several years. Composites of three monthly samples collected with the HASL wet/dry instrument were analyzed; the compositing was done to increase precision of the data. The total deposits of Pb and 210Pb in each of ten quarters from October 1976 through March 1979, in addition to the percent which came down dry, are tabulated. The obvious difference in the percent of the two substances represented by the dry fractions was not expected. The mean value of 30% for stable lead is in substantially good agreement with published data for Pb as well as for other metals in a variety of environments. The average of 7% for dry deposition of 210Pb, however, is lower than anticipated. Further, dry deposition of 210Pb reported from direct measurements as well as from estimates based on indirect methods ranged between 23% and 61%. The mean depositional flux of 210Pb over the period of these observations was 1.1 dpm per cm2 per year, in good agreement with previously reported observations and predictions. If it is assumed that the 210Pb dry fraction of 7% is anomalously low due to inefficient collection, and if it is presumed that it should be perhaps 35%, then the total 210Pb flux would have been about 1.5 dpm/cm2/yr