|
The remaining particle number concentration data in the three sections of
PARTICLE DIAMETER, © LL um: O19 ym: 93.6 vm
66 mBETWEEN SITES
ALL WINDS
|
fT ——0o 4100
p---9 swT0 Me
T
speed increments for air sampling.
:
170 TO 340° WINDS
6.1 m TOWER
if |-——v inetoz
Figure 13 (including the January 16 data) were determined using larger wind
170 10340 WINDS
29.9 m TOWER
p~—— = 4 3/21 10 5/20
616 10.715
f —~9 FA mM TOMER
E
a
-—0 66 1075
f
;
sore. ui’
L
pe?
SLOPES
oe
"
techniques minimized data point deviations around solid lines while
L
4
of wind speed.
J
The differences in exponents might be indicative of some
threshold wind speed near 4.5 m/sec above which soil more readily becomes
airborne.
NY
Differences in air concentrations were measured as a function of sampling
tower separation for the June 6 to July 5, 1974 data shown jn the right
portion of the figure. In this case, air was sampled simultaneously at a
500-m separation for 170° to 340° winds (winds from the west are 270°).
Upwind concentrations were greater except for the 1.1-um particle data
point at a wind speed of 5.8 m/sec.
The significant difference is that at
the upwind tower airborne concentrations increased with the first power of
wind speed while at the downwind tower airborne concentrations increased
with wind speed to the 0.6 and 3.2 power. Reasons for the differences
between upwind and downwind concentrations can only be hypothesized at
present. The differences are probably caused by different wind speeds at
the upwind and downwind towers, deposition of particles in the area between
towers,
and, probably of- most : significance, the. greater area of open soil
:
f
Ke
19 um
4
These
retaining a constant slope. Airborne soil concentrations increased with
either the 0.6th power (below 4.5 m/sec) or 3.2nd power (above 4.5 m/sec)
Ls ee
E
a
s
«
=
2=
The solid lines in each of the three
portions of the figure were calculated by least squares techniques.
iF
available for resuspension adjacent to the upwind tower.
Q
z
.
r
Average airborne mass loadings were calculated for A eoak wind speed (total
collected within impactors). Dust loading in ug/m3 are shown as a Function
of wind speed in Figure 14. Dust loadings ranged from 13 to 360 ug/m3,
As shown for two lines representing sampling times from March 4 to April 25,
1974, and May 6 to September 17, 1974, mass loadings for respirable particles
increased with wind speed to the 2.9th power for wind speeds greater than
4.5 m/sec.
ec
o'
.
i
Ht
tL
PP
r 36pm
& a
r
2
10 1
CONCLUSIONS
ye_
10 1
+
po tJ
WIND SPEED, misec
10 1
a
a
10
:
:
Particle resuspension rates are a function of at teast wind speed and
mechanical disturbances. Mechanical disturbances such as vehicular traffic
or a man walking can cause high local resuspension rates. In comparison,
average wind resuspension rates from a local area could be jess important
per unit area than local mechanical disturbance resuspension,
However,
wind-caused resuspension rates apply to the entire contaminated area.
If
one were to compare relative resuspension from wind-caused and mechanical
FIGURE 13.° Airborne Soil Particle Concentrations as a Function of
Particle Diameter, Wind Speed, Sampling Season, and
Sampling Site, 1974
2 04
disturbances, one would need to know the total surface contamination area
for wind resuspension versus sma!] localized surface contamination levels
205