138 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



amounts to an average of 0.62 nCi/min. Thus during this period about 10^ ^^^Pu-bearing 

 particles per minute were discharged from the 291-F stack to the environment. With a 

 flow rate in the stack of 2 x 10^ cfm, the average ^^^Pu-bearing particle concentration in 

 stack air was 5 particles/ft^ . 



EXHAUST 



o 



SUBMICROMETER 

 PARTICLES 



ATMOSPHERIC 

 DUST 



SOURCE 



LEAK 



SAMPLE 



Fig. 10 Formation of plutonium-bearing particles in exhaust systems by the coagulation 

 of submicrometer plutonium particles with atmospheric dust. 



Acknowledgment 



I gratefully acknowledge the assistance of E. F. Holdsworth and J. T. Armstrong of the 

 Chemistry Department of the Arizona State University, Tempe, Ariz., who performed the 

 electron-microprobe analyses. 



Appendix: Use of Elemental Enrichment Factors to Express Particle Compositions 



Background 



Two recent developments in aerosol studies have provided valuable tools for the analysis 

 of particle composition data. The first is the use of ratios of elemental concentrations 

 called "enrichment factors" to compare aerosol compositions. Begun in the early 

 seventies, this technique has gained wdde acceptance in the last few years (Rahn, 1971; 

 1976; Zoller, Gladney, and Duce, 1974; Duce, Hoffman, and ZoUer, 1975; Neustadter, 

 Fordyce, and King, 1976). The second development is the availability of data on the 

 composition of natural aerosols. In the last few years, Rahn (1976) published a 

 compilation of 104 data sets of trace elements in aerosols along with the geometric mean 

 and geometric standard deviation of the enrichment factors for each of the elements. 

 These data sets were from sampling sites ranging from highly industriahzed temperature 

 zones to the tropics and poles and represent all continents except South America as well 



