down the length of the tracer lane. With wind speeds of 3 to 4 m/s, pedestrian resuspension rates were from 1 x 10-5 to 7 x 10-4 fraction resuspended/ pass along the tracer lane, This pedestrian-generated turbulence was greater than wind stresses during the experiment. PA RTICLE RESUSPENSION RATES FROM ASPHALT AND CHEAT GRASS ROADS CAUSED BY VEHICLE PASSAGE er | TOT TT TT e-7 T TT A a jo TT Experimental values of wind-caused resuspension rates of tracer particles Tt —3 4 1 7 ” ovo ASPHALTROAD = 4 RB 10 L boil i 10 cL aranrir TRUCK, CHEAT GRASS ROAD 1 J 4 en I T 10 from environmental surfaces have not been experimentally determined from mass balance techniques other than for the present data (Orgill et al., 1976; Sehmel, 1975b; Sehme? and Lloyd, 1972, 1975b, 1976b, 1976c). Some data were initially obtained using 8-um mass medium diameter (MMD) ZnS particles and average wind speeds from 1 to 5 m/sec, More extensive data as a function of wind Speed were obtained using submicrometer CaMo04 particles. Average resuspension rates for ZnS particles were measured for resuspension from an asphalt surface (Sehmel and Lloyd, 1972) and a cheat grass surface (Sehmel, 1976). For average wind speeds of 1 to 4 m/sec, wind resuspension rates from an asphalt surface ranged from 5 x 10-9 to 6 x 10-8 fraction resuspended/sec. For average wind speeds of 1 to 5 m/sec, wind resuspension rates from a cheat grass surface ranged from 5 x 10-9 to 6 x 10-8 fraction resuspended/sec. Wind-caused resuspension was measured for submicrometer CaMo04 particles 7 10 qT TRUCK, ae ROAD te 10 ! ey FRACTION OF PARTICLES RESUSPENDED FROM ROAD PER VEHICLE PASS q Wind-Caused Resuspension 4 a tee 50 VEHICLE SPEED, mph deposited in a lightly vegetated area on the Hanford reservation shown in Figure 9. Tracer particles were deposited in a circular area of 23-m radius around the centrally located air sampling tower. Resuspended particles were measured at the tower as a function of wind Speed increments for respirable particte diameters and for nonrespirable particles at all wind speeds. Respirable particles were collected within particle cascade impactors (Figure 1) while nonrespirable particles were collected by impaction and gravity settling within cowls. ‘ Wind-caused resuspension rates are shown in Figure 10 as a function of wind speed. Resuspension rates ranged from about 10-1! to 10-7 fraction resus- pended/sec. Different functional dependencies of resuspension rates on wind speed can be obtained from these data, depending upon which set of wind speed increments are used. During the January to February period, air sampling was for large wind speed increments, while in subsequent experi- ments wind speed increments were smaller. The straight lines shown in Figure 10 were drawn through all data points. In these cases, resuspension rates increased with the 1.0 to 4.8 power of wind speed. However, when only data points for smaller wind speed increments are used, wind-caused resuspension rates increased with wind speed to the 4.8 power for 7, 3.3, 2.0, and 1.t-ym-diameter particles as well as for the smaller particles collected on the cascade impactor back-up filter. For comparable wind speed increments, tracer resuspension rates were nearly independent of the time the tracer was on the ground surface. FIGURE 8, Rate of Particle Resuspension Caused by Vehicle Passage Over Asphalt and Cheat Grass Roads 196 193 However, it