for mechanical disturbance resuspension rates. Both mechanisms, however,
do resuspend and transport potentially hazardous respirable particles.
Resuspensfon rates are needed for inclusion as source terms in atmospheric
diffusion and transport equations; however, model predictions are no better
than the uncertainty in the source data.
In the case of resuspension rates,
uncertainties are very Targe. Much research is yet needed to develop resus-
pension models to predict particle resuspensfon rates for any situation.
Wind-caused resuspension rates from a sparsely vegetated area have only been
TT
r
T
re
measured with submicrometer tracer particles.
The potential effect of different particies diameters on resuspension rates is unknown,
It might be
hypothesized that simflar results would be expected for other submicrometer
particles of interest since submicrometer particles are probably attached to
host soil particles when the particles are resuspended. If the particles of
interest were much larger, it is unknown whether the particles would be resuspended attached to host sofl particles or resuspended as discrete particles.
The change in airborne concentration of a pollutant as a function of time
is often attributed to a weathering half-life, the fixation of the pollutant
B
DUST LOADING, yg/m?
Le sLopes, u2?
5
particle into the ground surface soil.
of
i
5
order of years.
tions.
oo
+ o—————
s&—_—
6.1 m TOWER
29.9 m TOWER
7 116 T0288
& 3/21705/20
=---0 3/4104
Oo 64T075
—~O 56 T0 9/18
5 UPWIND
{6.1 m TOWER)
tree
10!
L
L_]
i
Lt
1
ut
i
1
l
l
ji Li
10
At the present time, credit for decreased airborne radioactivity
from resuspension could be attributed to a weathering half-life of months.
If a weathering half-life of years were applicable, the potential downwind
inhalation hazard from resuspended particles would be significantly increased.
Additional experimental data are needed to determine what weathering halflife should be used in hazards evaluations.
SAMPLING PERIODS (1974)
s——
Pr
Predictions using weathering half-lives of months versus
years could have a Significant implication in environmental hazards evalua-
{~~
a §——_—__—_
100
Vegetation on a resuspension surface will decrease resuspension rates. This
is rather obvious, but can be definitely concluded from decreased tracer
particle resuspension rates for vehicles driven on a cheat grass area compared to an asphalt area. Since vegetation does decrease resuspension, it
should be retained on all] areas of potential surface contamination and existing surface contaminated areas until] constructive cleanup operations can be
initiated.
WIND SPEED, m/sec
FIGURE 14.
Airborne Dust Loading Collected Within Impactors
as a Function of Wind Speed
. 206
For radioactivity, the weathering
half-life was on the order of 35 days. In contrast, weathering half-lives
for respirable tracer particles are now estimated here as being on the
207