High-resolution gamma ray spectroscopy has been used to obtain ratios of 214Bi to 214Pb specific activities for large volume air samples taken at a height of 20 m. Afternoon samples that were taken for a period of several months exhibited 214Bi/214Pb ratios that ranged from 0 to 2.2 with a mean value of 0.67¿0.06. Observed 214Pb specific activities for this group of samples ranged from 35.2 to 360.4 pCi/m3 with a mean value of 122.8 pCi/m3. Most samples exhibiting 214Bi/214Pb ratios greater than 1.0 were associated both with low values of 214Pb specific activity and with the advection of maritime air during the sampling period. When samples taken during strong winds are excluded, a mean 214Bi/214Pb activity ratio of 0.48¿0.08 is obtained. A smaller group of morning samples taken at the same location exhibited a mean 214Bi/214Pb ratio of 0.70¿0.08. The results of these measurements have been compared with the predictions of turbulent diffusion theory.