Silver Content of Precipitation from Seeded and Nonseeded Florida Cumuli

Abstract

Abstract A subprogram of NOAA's 1973 Florida Area Cumulus Experiment (FACE) was undertaken to determine the silver content of precipitation associated with convective clouds massively seeded with silver iodide nucleant over southern Florida. An atomic absorption analysis of 127 rainwater samples collected just below cloud base by a polypropylene-lined scoop mounted on the fuselage of the NOAA DC-6 aircraft indicated that the mean concentration of silver obtained on seed days (69 samples) was no greater (and, in fact, appreciably less) than that obtained on no-seed days (58 samples). In both sets of samples, the median concentration of silver was more than two orders of magnitude lower than the U. S. Public Health safety limit of 5 × 10−8 g ml−1. Of the 69 aircraft samples collected on seed days, only two contained a concentration of silver in excess of 1 × 10−9 g ml−1. Of the 58 aircraft samples collected on no-seed days, eight contained silver in concentrations exceeding 1 × 10−9 g ml−1. The samples coll...