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Abstract
The lead content of air, rainfall, and dry-fallout samples taken at several sites in Palo Alto, Calif, are reported and discussed. The high-speed high-density freeway traffic in the area appears to be the major source of lead pollution. The natural atmospheric cleansing processes of sedimentation and raindrop scavenging remove large quantities of lead particulate matter. It is suspected that nucleation occurs on the submicronic lead compound particles in the exhaust stream, producing droplets which may impact on the larger airborne particles. This could explain the wide range of size distributions reported in the literature as well as the large amounts of lead found in the samples analyzed.