Lead isotopes in North American coals are equally or much more radiogenic than those in the present continental crust (a mean composition for the continental crust is used). It is practicable to distinguish coal and gasoline lead pollutants by examining their isotopic compositions.

The concentrations of atmospheric lead around San Diego, California, have been determined and their geographic and seasonal variations are explained. The lead aerosol concentration at San Diego is increasing at a rate of 5 percent per year. The isotopic composition of lead aerosols is similar to that of the lead additives isolated from gasoline, which are the largest contributors to atmospheric lead pollution.

Procedures for the shipboard sampling of marine air and the analysis of its lead content by the isotope dilution method are discussed. Marine air collected over the north and central Pacific Ocean between California, Midway Island, and American Samoa showed a lead concentration range from 0.0003 to 0.0015 Mg. per cu. meter. This lead concentration range