FIELD TESTING AND EVALUATION OF DUST DEPOSITION AND ...

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models analyzed in this study is suited for estimating the interactions of particles with obstructions in the immediate vicinity of the source (i.e. at the junction of the unpaved road shoulder and the first row of vegetation downwind of the road). For estimating particle deposition in this region, it is preferable to use a technique similar to the one presented by Raupach and Leys (1999), who have developed a method to estimate the removal of particles by windbreaks. Their analysis is applicable to windbreaks of finite depth, but it may be possible to extend it to entire canopies with some modifications. 5.3 Summary Field experiments at the Ft, Bliss military facility indicated that for particles covered by the PM 10 size range, removal by deposition was not measurable at a distance of 100 m. This was confirmed by comparison with predictions by the ISC and the ADE models. Based on these findings, it was concluded that under neutral to unstable conditions in sparsely vegetated arid shrubland, which may comprise a large portion of the southwestern United States, removal of particles in the near source region by deposition is not an important consideration. The ADE model was found to over predict dispersion very close to the source (< 100 m), but the ISC concentration profiles fit the data reasonably well. One shortcoming of the ISC algorithm is the lack of ability to represent varying friction velocities. The turbulence behind moving vehicles was measured to quantify the height of the wake, termed the “injection height”. Using very simple analysis, it was determined that the size of the wake varies roughly linearly, by a multiple of 1.7, with the height of the vehicle. The injection height was found to have a large effect on the removal of particles downwind of an unpaved road, though only for stable atmospheric conditions. Comparison of emission factors measured at Ft. Bliss and those calculated according to the AP-42 guidance document (USEPA, 1999) indicated that by not accounting for vehicle speed, the AP-42 estimates are likely to be too high for vehicles traveling at low speeds. When only passenger-sized vehicles were considered, the Ft. Bliss data suggest that at 20 to 25 mph (a speed that is commonly assumed for unpaved road travel in emission inventories), AP-42 over predicts PM 10 emissions by 50%-100% compared to the measurements. When larger vehicles were included in the analysis, the AP-42 factors were in line with those measured for travel speeds of 20 to 25 mph. One reason cited for this apparent dependence on the distribution of vehicle size was the use of an aggregate-average weight in the AP-42 equation. The “lumped” weight approach is not self-consistent and is likely to result in inventories that overestimate the contribution of unpaved road dust to ambient PM 10 concentrations. This source of error should be addressed as part of the effort to reconcile emission inventories for geologically-derived PM 10 with the amount of crustal material found on filters measuring ambient concentrations. 5-24
6. DETERMINATION <strong>OF</strong> PARTICLE REMOVAL RATES UNDER STABLE CONDITIONS IN A MOCK URBAN SETTING As part of a DoD-funded study, the University of Utah measured vehiclegenerated road dust under stable atmospheric conditions at a flat site in the Utah west desert, and the horizontal flux of dust with the aid of interpolating functions that were fit to the wind speed and dust concentration measurements at discrete heights. The measured horizontal flux of dust and particle removal by deposition were compared to predictions by the one-dimensional Atmospheric Diffusion Equation (ADE) and the Industrial Source Complex (ISC) models. 6.1 Experimental Methods The field measurements were conducted at the Dugway Proving Ground, Tooele County, Utah in collaboration with the Mock Urban Setting Test (MUST), an atmospheric dispersion experiment funded by the Defense Threat Reduction Agency (Biltoft, 2001; Yee and Biltoft, 2002). The site is located at 40° 12.6' N, 113° 10.6' W and is 1310 m above sea level. The configuration, shown schematically in Figure 6-1, consisted of a 10 by 12 array of 2.5 m high by 2.4 m wide by 12.2 m long rectangular cargo shipping containers simulating buildings. The area surrounding the test site has a slope of 0.5 m / km rising to the south. Sand dunes 4-6 m high are 1 km to the north. Vegetation is a thin cover of brush (shadscale and black greasewood) 0.5 to 1 m high. The soil is classified by the Natural Resources Conservation Service (2000) as Skumpah silt loam and has 15% silt content. Screen analysis of a sample from the test road is provided in Table 6-1. 180 m 9 8 7 6 5 4 3 2 1 0 A B C D 176 m 4 E F G H I J 95 m 30 m 1 2 3 Y Unpaved Test Road X True North K 3 m L Figure 6-1. Plan view of the MUST site showing the array of shipping containers representing buildings and the location of the measurements. (1) 2-D sonic anemometers at 4, 8, 16 m; (2) DustTraks at 0.9, 1.7, and 3.7 m; (3) 3-D sonic anemometer at 1.6 m; (4) DustTraks at 1.8, 4.6, 9.1, and 18.3 m and 2-D sonic anemometers at 4, 8, 16, 32 m. 6-1
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FIELD TESTING AND EVALUATION OF DUS
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EXECUTIVE SUMMARY The Western State
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models. Countess (2001) summarized
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TABLE OF CONTENTS 1. INTRODUCTION 1
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TABLE OF FIGURES Figure 2-1. Develo
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Figure 4-6. The fraction of particl
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Figure 5-16. Comparison of fraction
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LIST OF TABLES Table 2-1. Parameter
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1. INTRODUCTION 1.1 Background The
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2.BACKGROUND Fugitive dust is emitt
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Planetary Boundary Layer (PBL) F =
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C D u* = ur The overall drag c
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St a vg u g = cA L * Equation 2
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Table 2-1. Parameters used in the S
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1E+01 1E+00 z0 = 4.4 cm z0 = 6.4 cm
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pathway for deposition for particle
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An alternative method for modeling
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3. MEASUREMENT OF DEPOSTION VELOCIT
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Department at the University of Uta
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In the laboratory, the deposited ma
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Table 3-2. Log of all flat substrat
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16 Normalized Deposition Velocity 1
Page 47 and 48: 1.E+05 Deposition Velocity - cm/s 1
Page 49 and 50: are deposition from a horizontally
Page 51 and 52: single element that is intended to
Page 53 and 54: 4. MODELS USED TO STUDY PARTICLE RE
Page 55 and 56: κu ( ) * z 8 fz K zz = exp −
Page 57 and 58: C = −6 ( 1× 10 ) QV 2π u s σ
Page 59 and 60: oad. M is the mass of particles in
Page 61 and 62: By making the approximation that dm
Page 63 and 64: diameters less than 10 microns. Dis
Page 65 and 66: of such a height is somewhat arbitr
Page 67 and 68: 1 0.9 0.8 1 0.9 0.8 Fraction remain
Page 69 and 70: Fraction of Particles Remaining in
Page 71 and 72: gravitational settling. Stable cond
Page 73 and 74: though it is expected to improve at
Page 75 and 76: 5. DETERMINATION OF PARTICLE REMOVA
Page 77 and 78: PM 10 measured by the DustTrak must
Page 79 and 80: 100% 90% 80% Relative Frequency (pr
Page 81 and 82: average wind speed measured at 12 m
Page 83 and 84: where the subscript i indicates tha
Page 85 and 86: k C int = peakend k C peeakstart d
Page 87 and 88: Height z (m) 14 12 10 8 6 T1_data T
Page 89 and 90: Horizontal fluxes of PM 10 measured
Page 92 and 93: Table 5-2 enumerates the speed-depe
Page 94 and 95: 6 Ratio of AP-42 Emission Factor to
Page 96 and 97: to the ground) giving an approximat
Page 100 and 101: Table 6-1. Screen analysis of test
Page 102 and 103: value which was used up to the midp
Page 104 and 105: measured at 3,1. Downwind the dust
Page 106 and 107: trips, the average readings for the
Page 108 and 109: Fraction of particles of stated siz
Page 110 and 111: the ground, where particles have a
Page 112 and 113: particles through the top of the bo
Page 114 and 115: deposition. Much of the decrease in
Page 116 and 117: 7-8
Page 118 and 119: Gifford, F.A. (1961). Use of Routin
Page 120: Venkatram, A. (1993). The Parametri
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