Simultaneous measurements of airborne plutonium-239 and americium-241 concentrations have not been reported outside of exclusion areas. Resuspension studies to date do not suggest differences in resuspension for different radionuclides, but data are limited. Simultaneous measurements of airborne concentrations of both plutonium~239 and americium-241 would indicate similarities which might be expected for different transuranics. Thus, the objectives of this study were to measure simultaneously both plutonium-239 and americium-241 airborne concentrations and fluxes on both nonrespirable and "small" particles for sampling heights up to 122 nm. SAMPLING SITE The sampling site was at the 125 m meteorological tower located outside the exclusion area on the Hanford area. This site is approximately one km east of the 200W Separation Area fence. Air sampling equipment was located at heights of 1.9, 15, 30, 61, 91, and 122 m. EXPERIMENTAL PROCEDURE Air sampling was continuous for all wind speeds and directions for the time period between August 13 and November 12, 1976. Air sampling was with the impactor cowl system shown in Fig. 1 (Sehmel, 1973). The 15 cm diameter cowl inlet was continuously directed into the wind by the wind orientation tail fin. Most of the larger particles (greater than about 10- to 20-um diameter) entering the inlet subsequently settled within the cowl body. Some larger particles were also collected inside the particle cascade impactor (Sehmel, 1973; Willeke, 1975). Interstage loss particles within the cascade impactor which are retrieved by light brushing are of nonrespirable size. It will be assumed all nonrespirable particles entering the impactor are collected as interstage loss particles. The fraction by weight and by plutonium content of these nonrespirable particles on impactor stage collection is considered to have a minimal influence on the general conclusion of this study. Particles collected within the cowl plus impactor interstage loss parti- cles are called "large" cowl-collected particles. Cowl-collected parti- cles are assumed to have been collected independent of the air sampling rate. Although the "small" impactor-collected particles are an index to the respirable airborne particle concentrations, these small particles do contain some nonrespirable particles. These small particles include all 708