-14- 1 I I I ,, 1 1 I 530 .- 500 400 300 c“’ 200 100 c I o I I 5 I 1 10 I I 15 I J 20 . Time, s Figure 4. An example of a dust concentration pulse on the downwind side of dirt road following passage of a light motor vehicle, a one-lane 11:05 a.m., May 15, 1978 (wind speed 4.5 m S-l). s .. (_