REVIEW OF RESUSPENSION MODELS 223 



same technique appear to increase as the 2.9 power of the wind speed for the higher wind 

 speeds (Sehmel, 1977c). 



The data from the backup filters, wliich showed an increase as the 4.8 power of the 

 wind speed and for which both the small interval and wide interval of sampling fitted the 

 curve, gave a fit to 



RR= 1.96X 10"'^ u*-^^ (16) 



where RR is the resuspension rate. If one assumes that the logarithmic wind profile 

 existed throughout the period, this becomes 



RR = 2 X 10-*^ ut-^2 (17) 



when the threshold velocity is ignored. 



Sehmel (1972) also measured the resuspension rate of zinc sulfide tracer particles 

 from an asphalt surface. Average resuspension rates were determined to range from 

 5 X 10~^ to 6 X 10~* sec~^ for average wind speeds from 2 to 9 mph (0.9 to 4.2 

 m/sec). The dependency of resuspension rate on wind speed was not determined, but 

 there was some indication that wind gusts greater than about 15 mph (7 m/sec) rapidly 

 suspended particles. 



In a similar experiment but in an area of cheatgrass, a resuspension rate of 



3.4 X 10~^ sec~^ occurred in an area of surface roughness of 4 cm and a friction 

 velocity of 0.52 m/sec (Sehmel, 1976b). After truck traffic that removed 0.35% of the 

 ZnS, the surface roughness was reduced to 3 cm, and a resuspension rate of 1 .25 x 10^^ 

 sec~^ was measured in a friction velocity of 0.5 1 m/sec. 



Sehmel (1975) measured the resuspension rate of 10-/im-diameter uranine particles 

 deposited on the inner surface of an aluminum tube with a 2.93-cm inside diameter. The 

 resuspension rates ranged from 10~^ to 10~^ sec~^ and were dependent on airflow rates 

 and resuspension time. Orgill, Petersen, and Sehmel (1976) measured the resuspension of 

 DDT from forests in the Pacific northwest. The DDT was sprayed in the early morning 

 with low wind speeds, and sampling was conducted by an aircraft -mounted sampler for 5 

 days. Calculated resuspension rates on three of the sampUng days were 1 .0 x 10~^, 



2.5 X 10"^ and 7.7 x 10"^ Sehmel (1976b; 1977c) proposed a correlation between 

 resuspension rate and the roughness height Zq using the data from the experiments on the 

 aluminum tube, the ZnS from the asphalt surface, the molybdenum tracer from desert 

 soil, and the DDT from the forest. This curve shows a decrease in resuspension rate from 

 the aluminum-tube data to the molybdenum tracer with the asphalt surface falling on the 

 Unes between these two points. However, the DDT from the forest, with a large roughness 

 height, had an increase by 2.5 orders of magnitude from the soil data. It is not clear how 

 these resuspension-rate data were corrected for the differing wind speeds or values of u^^ 

 that existed in each of the experiments. It is further noted that the surfaces and, possibly, 

 mechanisms of wind pickup from the surface were different. For example, the 

 resuspension of DDT from the forest could have been primarily a result of the mechanical 

 movement of leaves, needles, and branches rather than the types of force found on the 

 soil surface. 



There have been many measurements of the air concentration in or near an area 

 contaminated with radioactive materials, but most of these are not suitable for estimating 

 resuspension rates or dependency on wind speed because of the lack of detailed 

 meteorological data at the time of the measurement or the lack of a detailed knowledge 



