particle collection on each cascade impactor stage except for interstage loss particles. Particles were sampled at a flow rate of 0.57 m?/min and those found on the stages were assumed to be without inertia with respect to sampling efficiency. Thus, small particles were assumed to have followed the sampled air into the cascade particle impactor. For radiochemical analysis, particles collected as interstage losses in the impactors were combined with the large cowl particles. After sample collection, the impactor* Type "A" fiberglass stage collectors were equilibrated with laboratory humidity (approximately 50% relative humidity), weighed, and all stages and backup filter combined into one "small" particle sample. Particles collected within the cowl and interstage loss particles were brushed off for collection, weighed, and combined into one sample. These "small" and "large" particle samples were analyzed** for plutonium-239 and americium-241. HORIZONTAL FLUX CALCULATION Average horizontal airborne plutonium-239 and americium-241 fluxes were calculated from the collected small and large particles. Fluxes are in units of pCi/(m@ day) for both large and small particles. Two isokinetic sampling assumptions were made for these calculations: (1) for large particles, particle inertia was assumed sufficient to cause particle collection within the cowl inlet for all wind speeds; and (2) for small particles, particles were assumed to be without inertia and followed airflow. For large particles, the flux was calculated from the uCi collected in the cowl (plus interstage impactor loss) divided by the product of cowl inlet cross-sectional area and sampling time. For small particles, the flux was calculated from the product of measured airborne concentration per unit air volume sampled in the impactor, uCi/em3, and average wind speed at each sampling height. The average wind speed at each height was: 1.6 m/sec at 1.9 m; 2.9 m/sec at 15 m; 3.4 m/sec at 30 m; 3.7 m/sec at 61m; 3.8 m/sec at 91 m; and 4.0 m/sec at 122 nm. RESULTS AND DISCUSSION Airborne plutonium~239 and americium-241 concentrations per unit air volume, concentrations per gram of airborne solid, and horizontal fluxes *Andersen 2000, Inc., Model 65-100 High-Volume Sampler Head, P.O. Box 20769, AMF, Atlanta, Georgia 30302 *kLFE Environmental Laboratories, Richmond, California. 710