Lead Measurement in Urban Air As It Relates to Weather Modification

Abstract

Results from measurements made to study the behavior of lead aerosols in Denver urban air as latent ice nuclei are discussed. In the study, use was made of three independent measuring systems. These were: 1) an NCAR continuous ice nucleus counter with a capability to convert suspended lead compounds to lead iodide particles prior to passage through the cloud chamber and counting unit, 2) an atomic absorption spectrophotometer for analysis of lead content in collected air and rain water samples, and 3) the use of Tufts? spot test for obtaining lead particle concentration and size distribution from collected Millipore filters. Both ground and airborne measurements were made. Pertinent findings included: 1) good Qualitative agreement among the three types of measurements; 2) lead content of rain water an order of magnitude greater than silver concentration in seeded snow samples which were collected in a weather modification seeding target area using silver iodide as the seeding agent; and 3) 10-300 lead particles (latent ice nuclei) liter?1 existing up to 9000 ft above the surface when unstable temperature stratification existed and which were converted into active ice nuclei (lead iodide particles) when passed through an iodine vapor chamber.