FIELD TESTING AND EVALUATION OF DUST DEPOSITION AND ...

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where D p is the particle diameter, ρ p is the particle density, g is the gravitational constant, µ is the viscosity of air, and C c is the Cunningham slip correction factor, C c 2λ 1.1D = + + − p 1 1.257 0.4exp D 2 λ p Equation 2-5 with λ equal to the mean free path of air molecules. 2.1.1 The Model of Slinn (1982) In a seminal paper, Slinn (1982) described the framework for a model to predict particle dry deposition to vegetative canopies. The model is based on the mass balance expression ∂ ∂C = z Κ ∂ ∂z ( c αu) C d ξ c Equation 2-6 where K is the turbulent diffusivity in the vertical direction, C is the mass or number concentration of particles, c d is the average drag coefficient for vegetation, α is the surface area of vegetation per unit volume, u is the mean wind speed, and ξ c is the canopy element collection efficiency for particles. The LHS of Equation 2-6 represents the flux of particles through a horizontal plane located at a height z above the ground while the RHS is the removal rate of particles by dry deposition. It is implied in the form of Equation 2-6 that turbulent dispersion only serves to bring particles from high above the canopy towards the ground. Practically, this means that the particle concentration profile above the vegetative canopy is well-developed and at steady state (i.e. not changing in time). This situation corresponds strictly only to Region C in Figure 2-1. However, if the deposition rate calculated is assumed to apply only locally (i.e. not constant in the downwind direction), then we may extend the applicability of Equation 2-6 into Region B. The final form of the deposition velocity provided by Slinn (1982) includes a term to account for gravitational settling: v d = v g + C D uh ur 1 + ur ξ + 1−ξ ξ tanhγ ζ −1 Equation 2-7 where C D is the overall drag coefficient for the canopy, u h is the wind speed at the top of the canopy (h being equal to the canopy height), u r is the wind speed at some reference height z r above the canopy, ξ is the location-independent canopy collection efficiency, and γ is a parameter that characterizes the wind profile within the canopy. 2-4
C D u* = ur The overall drag coefficient C D is given by 2 Equation 2-8 where u * is the friction velocity which may be estimated if the velocity profile above the canopy is approximately logarithmic with either u − = * z d u( z) ln κ z0 or u z) = u * ( r u zr − − ln κ z − ( h − l) ( ) h − l Equation 2-9 Equation 2-10 where κ is the von Karman constant and is equal to 0.4, d is the displacement height, z 0 is the roughness height, h is the canopy height, and l is the length scale of turbulence at the top of the canopy. The displacement height d can be thought of as the height above which the velocity profile is expected to have a logarithmic shape. Under some conditions, the displacement height and the roughness height z 0 may be difficult to estimate. For this reason, it may be preferable to use Equation 2-10, which utilizes characteristics of the canopy, namely the canopy height and the length scale of turbulence at the top of the canopy. Slinn suggests the approximation d = h − l . The ratio u h /u r in Equation 2-7 is given by Equation 2-9 with h-d=l Equation 2-11 u u h r = u * l ln κur z 0 Equation 2-12 or by Equation 2-10: u u h r = u z − ln u κ 1 * r r ( h − l) − l . Equation 2-13 2-5
Page 1: FIELD TESTING AND EVALUATION OF DUS
Page 5 and 6: EXECUTIVE SUMMARY The Western State
Page 7 and 8: models. Countess (2001) summarized
Page 9 and 10: TABLE OF CONTENTS 1. INTRODUCTION 1
Page 11 and 12: TABLE OF FIGURES Figure 2-1. Develo
Page 13 and 14: Figure 4-6. The fraction of particl
Page 15 and 16: Figure 5-16. Comparison of fraction
Page 17 and 18: LIST OF TABLES Table 2-1. Parameter
Page 19 and 20: 1. INTRODUCTION 1.1 Background The
Page 21 and 22: 2.BACKGROUND Fugitive dust is emitt
Page 23: Planetary Boundary Layer (PBL) F =
Page 27 and 28: St a vg u g = cA L * Equation 2
Page 29 and 30: Table 2-1. Parameters used in the S
Page 31 and 32: 1E+01 1E+00 z0 = 4.4 cm z0 = 6.4 cm
Page 33 and 34: pathway for deposition for particle
Page 35 and 36: An alternative method for modeling
Page 37 and 38: 3. MEASUREMENT OF DEPOSTION VELOCIT
Page 39 and 40: Department at the University of Uta
Page 41 and 42: In the laboratory, the deposited ma
Page 43 and 44: Table 3-2. Log of all flat substrat
Page 45 and 46: 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
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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 98 and 99:
models analyzed in this study is su
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
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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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