SPRINGTIME DUST AEROSOLS AT WHITE SANDS MISSILE RANGE, NEW MEXICO

1
SPRINGTIME DUST AEROSOLS AT WHITE SANDS MISSILE
RANGE, NEW MEXICO

• Catherine F. Cahill, Geophysical Institute and
  Department of Chemistry, University of Alaska
  Fairbanks, Fairbanks, AK 99775
• Young Yee, Atmospheric Effects Branch, Army
  Research Laboratory, White Sands Missile Range,
  NM 88002
• Thomas E. Gill, Alfredo Ruiz and Sonny P. Emmert,
  Department of Geological Sciences, University of
  Texas at El Paso, El Paso, TX 79968
• Thomas A. Cahill, Delta Group, University of
  California at Davis, Davis, CA 95616
• Fred Wilson and Edward Ellison, Meteorology
  Branch, White Sands Missile Range, NM 88002

Abstract Windblown dust on the battlefield can
create a hazardous environment for personnel and
equipment. Current dust models, such as CARMA,
are used to predict the aerosol loading in
operational theaters. However, size-fractionated
aerosol measurements are needed to improve and
validate the aerosol generation portions of the
models. Therefore, from April 19 through May 23,
2005, two size-fractionated (8 size bins between
10 and 0.09 mm in aerodynamic diameter) aerosol
samplers were deployed upwind and downwind of a
playa at the White Sands Missile Range in New
Mexico to collect aerosols samples to help
determine the size and amount of dust aerosols
generated as a function of wind speed. The
aerosol samplers were co-located with
meteorological sensors and dust collectors. The
meteorological data for the sampling period,
including wind speed and direction, was provided
by the Meteorological Division of the White Sands
Missile Range. The mass and optical absorption
of the aerosols collected is correlated with wind
speed and other meteorological parameters to
determine the emission, as a function of size, of
dust aerosols at different wind speeds. This
data will be used to initialize and/or validate
dust models such as CARMA, calculate the
visibility degradation associated with a given
aerosol loading, help evaluate sensor performance
in dusty environments and determine the effects
of dust loading on personnel and equipment.
Purpose Use size-fractionated, time-resolved
aerosol samplers at two locations (one upwind of
the other) to obtain information on the
production of aerosols as a function of
meteorological conditions. These aerosol
measurements will be used to improve and validate
dust evolution models. Sampling Sites The two
sites selected for the experiment were Space
Harbor (a.k.a. the Northrup Strip) and Tularosa
Gate (a.k.a. ABC-1). Figure 1 shows the site
locations. The two sites were selected because
Tularosa Gate is downwind of Space Harbor and a
large expanse of white sand dunes.

• Results
• The Space Harbor site is located on a dry, flat,
  barren lake bed composed of tiny gypsum (calcium
  sulfate) crystals which are subject to frequent
  resuspension by the spring winds into strong sand
  and dust
• storms. Space Harbor was clearly an aerosol
  source area during the study period (Figure 6).
• Due to heavy spring rains in the Southwest, the
  terrain around the Tularosa Gate site was more
  widely vegetated than usual, and the sand dunes
  in the area were largely stabilized by
  vegetation. No detectable amounts of
  near-surface coarse dust and sand were collected
  in the BSNE samplers at Tularosa Gate. This
  strongly suggests that the Tularosa Gate location
  was only a receptor site for dust aerosols and
  not an active source during the study period.
  Figures 5, 6, 8 and 9 show higher concentrations
  of dust aerosols at Space Harbor representing
  episodic spikes of intense wind resupension in
  and around the site, while aerosol concentrations
  were lower and more spread out in time at
  Tularosa Gate, which acted as a receptor site.
• The overall proportion of fine, loose,
  resuspendable particles on the soil surface at
  White Sands is lower than that at other locales
  studied by the investigators. For example, less
  than 1 by mass of particles with aerodynamic
  diameters less than 10 um in diameter at Space
  Harbor compared to up to 40-50 at Owens Lake,
  California and 10-30 at Lubbock, Texas.
  However, the White Sands are composed of gypsum
  crystals, which are extremely soft and brittle
  and probably much more easily fractured into fine
  particles in strong winds than the soil of other
  terrains. In addition, the Space Harbor site
  (Lake Lucero's dry bed) is flat and unvegetated
  (extremely low roughness) and an extremely
  intense source of blowing dust and sand
  satellite images denote many major dust storms
  originate in this area and the huge White Sands
  dune field is comprised of sand blown by the wind
  from Lake Lucero (Space Harbor). The relatively
  low proportion of dust-sized materials in the
  source area may be more than compensated by the
  intensity and size of the source.
• Space Harbors aerosol peaks do not always
  correspond to peaks at Tularosa Gate (Figures 7
  and 8). This is reasonable given that Space
  Harbor has more periods of higher wind speed than
  Tularosa Gate (Figure 10), Tularosa Gate is not a
  source area (only a receptor site), and given the
  mountainous topography of the region and the
  terrain variations of the White Sands range,
  particles produced at Space Harbor may not have
  been transported in the direction of Tularosa
  Gate. Many of the high wind events during the
  study period were associated with localized
  thunderstorm activity with variable and ephemeral
  wind patterns (rather than synoptic systems with
  areally consistent wind directions), also
  suggesting a possible decoupling between the two
  sampling sites.
• For similar wind speeds, Tularosa Gate has
  smaller aerosol peaks in the larger DRUM size
  fractions than Space Harbor (Figures 6, 9 and
  10), again illustrating the behavior of Space
  Harbor as a source and Tularosa Gate as a
  receptor site. Also note that while aerosols
  generated at the source area (Space Harbor) could
  best be described as sandstorms at the Space
  Harbor site, collision, coalescence, and/or
  fallout processes within the aerosol cloud as it
  was advected downwind from and out of that source
  area (towards Tularosa Gate) could lead to the
  aerosol having very different particle size
  characteristics at downwind receptor sites.
  Fallout of the airborne sand particles in the
  near-downwind (this is, after all, exactly what
  is believed to have built the White Sands dune
  field located downstream of Space Harbor) would
  leave the dust component remaining suspended for
  longer-range transport fracture-inducing
  collisions between sand grains and further
  desiccation of the grains during transport within
  the dry sand cloud could break sand grains and
  clumps into finer (dust) particles as it moved
  downstream.
• A preliminary analysis of wind direction shows
  that most events showing high aerosol mass
  concentrations at both sites correspond with
  winds coming from 225o, in which case Tularosa
  Gate is downwind of Space Harbor. Also, the
  preliminary analysis suggests that relative
  humidity may be having a dampening effect on the
  dust evolution. Particle size tests of the
  surface soils indicate that the wet gypsum
  agglomerates (clumps together) when moist, rather
  than dispersing (breaking apart) like many soils
  (Figure 11 and Tables 1 and 2). In dry air,
  Space Harbor surface sediments contained 1.25
  (by volume) particles smaller than 5 microns and
  6.12 particles smaller than 10 microns, with a
  peak near 70 microns (very fine sand) and only
  0.06 coarse sand. The suggested effect of
  humidity on observed aerosol concentration at
  White Sands is probably related to this property
  of the gypsum soil.
• The orange-colored material observed in the
  largest DRUM size fractions at Space Harbor does
  not appear to be the white gypsum we expected.
  Therefore, it appears that some other source is
  impacting the larger size fraction aerosols at
  Space Harbor. The chemical composition of this
  material will be determined and use to identify
  potential sources.
• The black material observed in the 0.26 to 0.09
  mm DRUM size fraction at Tularosa Gate is
  probably emissions from a diesel engine.
• Conclusions

Inlet to 5.0 mm ?
Inlet to 5.0 mm ?
0.26 to 0.09 mm ?
0.26 to 0.09 mm ?
Figure 5. A photo of the Sand Harbor DRUM
samples. Note the orange-colored bands in the
largest size fractions.
Figure 8. A photo of the Tularosa Gate DRUM
samples. Note the strong black band in the
smallest size fraction (probably diesel
emissions) and the weaker banding in the large
size fractions.
Figure 6. The aerosol mass corresponding to the
Sand Harbor DRUM samples in Figure 5 results.
Figure 9. The aerosol mass corresponding to the
Tularosa Gate DRUM samples in Figure 8.

Figure 7. A comparison between the 2.5 to 5.0 mm
aerosol mass concentrations at Space Harbor and
Tularosa Gate.
Figure 10. Time series of wind speeds at Space
Harbor and Tularosa Gate.
Figure 1. A satellite photo and pictures showing
the sampling sites.
Experimental Methods April 18 through May 23,
2005, two DRUM aerosol impactors (Figure 2) were
deployed at Space Harbor and Tularosa Gate. The
samplers continuously collected aerosols in eight
size fractions between the inlet (15 mm) and
0.09 mm in aerodynamic diameter. The aerosol
samplers were co-located with SAMS meteorological
stations at both sites. At Sand Harbor a passive
blowing dust/sand (BSNE) sampler (Figures 3 and
4) collected large (dust and sand sized)
particles suspended by the wind. Surface soil
samples were collected at each site at the start
of the study.
Space Harbor
Tularosa Gate
Figure 8. A visual comparison of the 2.5 to 5.0
mm aerosol sample strips. The mass
concentrations for these strips are shown in
Figure 7.
Figure 11. This figure illustrates how the Space
Harbor surface soil particles aggregated (clumped
together) when moist. The dry soil (green line)
has smaller particles than the wet soil (red
line).
Table 2. Space Harbor Surface Soil Layer particle
size distribution, WET SIZE (microns)
OF TOTAL SAMPLE BY VOLUME 0.1 to
1.15 0.00 1.15 to 2.5 0.02 2.5
to 5.0 0.50 5.0 to 15.0
2.19 15.0 to 50.0 8.84 silt 50.0 to
100.0 15.42 very fine sand 100.0 to 250.0
27.99 fine sand 250.0 to 500.0 20.49
medium sand 500.0 to 1000.0 17.91 coarse
sand 1000.0 to 2000.0 6.66 very coarse
sand
Table 1. Space Harbor Surface Soil Layer particle
size distribution, DRY SIZE (microns)
OF TOTAL SAMPLE BY VOLUME 0.1 to
1.0 0.06 1.0 to 2.0 0.46 2.0 to 5.0 0.73 5.0 to
10.0 4.87 10.0 to 50.0 silt 26.07 (note 10.0
to 20.0 is 6.87) 50.0 to 100.0 45.25 very fine
sand 100.0 to 250.0 17.80 fine sand 250.0 to
500.0 4.66 medium sand 500.0 to 1000.0 0.06
coarse sand gt1000.0 ND
Figure 2. A DRUM aerosol impactor.
Figures 3 and 4. A schematic of a BNSE and a
picture showing a deployed BNSE.
Table 3. Bulk Airborne Deposition (dust and sand)
measurements collected 5 cm above the ground
surface in the BSNE sampler at Space Harbor from
the start of the study until 05/05/05.
SIZE (microns) OF
TOTAL SAMPLE BY VOLUME 0.1 to 1.15
0.00 1.15 to 2.5
0.00 2.5 to 5.0
0.11 5.0 to 15.0
1.12 15.0 to 50.0
8.84 silt 50.0 to 100.0
4.49 very fine sand
100.0 to 250.0 13.48 fine
sand 250.0 to 500.0
42.70 medium sand 500.0 to 1000.0
9.74 coarse sand
1000.0 to 2000.0 0.51 very coarse
sand
Analytical Methods All results presented in this
poster are preliminary. The DRUM aerosol
samples were analyzed for mass concentration by
b-gauge. Specific stages will be analyzed by
Ultraviolet-Visible spectroscopy for optical
absorption as a function of wavelength and
Synchrotron X-Ray Fluorescence (S-XRF) for 42
elements between sodium and uranium. The
particle size of soil and BSNE samples was
determined by laser diffraction. These samples
are also being analyzed by ion chromatography for
anion and cation content, and standard methods of
soil analysis for electrical conductivity, pH,
and organic carbon content. Elemental analysis
of these samples will be performed by inductively
charged plasma mass spectrometry and/or S-XRF.