FIELD TESTING AND EVALUATION OF DUST DEPOSITION AND ...

3. MEASUREMENT OF DEPOSTION VELOCITY
The goal of this WESTAR-funded, University of Utah subproject was to estimate
the magnitude of particle deposition from vehicle-generated dust clouds downwind of an
unpaved road. In this chapter, we discuss the methods and results of direct measurement
of deposition velocity v d . Measurements were conducted in the “impact zone” (refer
Figure 2-1). The measured values of v d are compared to values previously reported in the
literature and analyzed in the context of the resistance model for deposition.
Two types of surfaces for particle deposition, flat substrates and artificial
vegetation, were analyzed with microscopic and gravimetric techniques. Comparison of
these measurements with prior work suggests that there are challenges to bridging direct
measurements with canopy-wide deposition velocities.
3.1 Methods
All the deposition velocity testing was conducted during April 2002 at Ft. Bliss
TX, on a spur road south of Loyalty Lane at GPS coordinates 13 3 70 544 E, 35 28 119
N. The field experiments were conducted in cooperation with the SERDP-funded
projects CP1190 and CP1191. The site is arid with sparse vegetation cover and exposed
sand. The prevailing winds were from the west and nearly perpendicular to the road.
Road surface samples were collected and size distribution was measured by standard
sieve analysis (refer Table 3-1).
Table 3-1 Cumulative screen analysis for the soils samples collected before and after the sampling
period
Facility & GPS Units/
Sample Site Location
Well Test
Road
13 3 70 544 E
35 28 119 N
DRI/JMV ID Notes Silt %
+ 3/8 + 4 + 20 + 30 + 50 + 100 + 200 - 200
mesh mesh mesh mesh mesh mesh mesh mesh
Heavy sand deposits
K408-1A from previous day’s 7.0 1.00 1.00 1.00 0.97 0.85 0.64 0.36 0.07
windstorm
Well Test
Road
13 3 70 544 E
35 28 119 N
K419-TR-1
After extensive driving
compared to previous 4.1 1.00 0.99 0.98 0.87 0.81 0.59 0.28 0.04
samples
Dust Concentration was measured using a GRIMM (Dust Monitor Series 1.108®,
GRIMM Technologies Inc., Douglasville, GA), which recorded particle-count
concentration for 16 size ranges logging every six seconds. This is an optical instrument
that determines particle size and count by light scattering. The sample inlet was placed
next to the surfaces used for particle deposition sampling. A 2.5 m long PVC tube
connected the inlet to the GRIMM instrument, which was placed with the data-logging
computer in a sealed box. One test was conducted using a different GRIMM that had a
direct sample inlet and that was programmed to report calculated mass. Quality checks
for the GRIMM included an internal calibration cycle and cleaning of sample inlet head.
The data from the GRIMM were used to obtain a particle number size distribution timeaveraged
over the duration of each dust deposition experiment.
3.1.1 Deposition on Flat Substrates
A series of tests was conducted to measure the passive deposition of vehicle
generated dust particles on flat surfaces placed near the road. The technique involved
3-1