222 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



400 600 800 



SOIL-ERODIBILITY INDEX 



Fig. 2 Tentative relation for parameterization of dust flux for the Gillette-Shinn 

 model. 



the ground was 0.62 g of molybdenum per square meter. Measurements were made with a 

 cowled impactor, which always faced into the wind, at heights to 6.1 m; some 

 measurements were made at specific wind speeds as measured at a height of 2.1 m above 

 the ground. Resuspension rates were calculated from a mass balance calculated from the 

 profile. Those particles depositing in the cowl were considered as "nonrespirable," and 

 those entering the impactor were considered as "respirable." The impactor separated the 

 respirable particles into nominal diameters for unit-density spheres of 7, 3.3, 2.0, and 1 .1 

 /nm and smaller particles on the backup filters. 



In these experiments the resuspension rates ranged from about 10~^ ^ to 10~^ sec~^ 

 (Sehmel, 1977a). Hots of all the data showed that the resuspension rates increased with 

 the 1.0 to 4.8 power of the wind speed. However, these results included wind intervals 

 with wide speed increments; thus an uncertainty as to the actual wind speed to be used 

 existed. When these intervals were eUminated, the resuspension rates for all sizes in the 

 impactor and the backup filter increased with wind speed to the 4.8 power. It may be 

 noted, however, that these experiments were run over a finite period of time; so 

 differences in stability would occur. This would cause differences in the wind profile and 

 a change in u^:. Thus, if the majority of the lower speed winds were in the stable 

 condition, where u* would be lower than for the neutral condition, and if the majority of 

 the higher speed winds were in the unstable condition, where u* was greater than for the 

 neutral condition, an exaggeration of the slope of the curve would occur. Since lower 

 wind speeds frequently occur in the stable condition and higher wind speeds in the 

 unstable condition, it can be postulated that such an effect has influenced these 

 relationships, albeit to an unknown degree. It is noted, however, that dust loadings by the 



