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