FIELD TESTING AND EVALUATION OF DUST DEPOSITION AND ...

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1E+01 1E+00 vd (cm/s) 1E-01 1E-02 1E-03 1E-03 1E-02 1E-01 1E+00 1E+01 1E+02 Dp (microns) Figure 2-3. Deposition velocity vs. aerodynamic particle size using Slinn's (1982) model. See Table 2-1 for parameters used. 1E+01 Etotal, Ebrownian, Einterception, Eimpaction 1E+00 1E-01 1E-02 1E-03 E_total E_Brownian motion E_Interception E_Impaction 1E-04 1E-04 1E-03 1E-02 1E-01 1E+00 1E+01 1E+02 Dp (microns) Figure 2-4. Contributions of Brownian motion, Interception, and inertial impaction to the total removal efficiency. See Table 2-1 for parameters used. RHS of Equation 2-3 for particles larger than 10 µm and for particles between 1 µm and 10 µm under low wind conditions. It is clear from examination of Table 2-1 that use of Slinn’s model requires the specification of a number of parameters that may not be available. For example, the parameters F s , A s , A L , c, b, and c v /c d are generally unavailable for a wide range of vegetative covers. These parameters are roughly estimated by a best-guess approach. Figure 2-5 illustrates the sensitivity of the model with respect to uncertainties in these parameters. The Figure is confined to the vicinity of the particle size range relevant for PM 10 dust. F s and A s only affect the deposition velocity through the interception term E IN (Equation 2-16). Since interception is a minor pathway for super micron particles, the effect of varying these two parameters is small. In contrast, changing the size of A L from 1 mm to 0.5 mm measurably improves the impaction efficiency and the overall collection efficiency. It is unclear how the coefficient b should be chosen for a given canopy. Rebound for particles with diameter less than ≈ 5 µm appears to be a minor consideration. The effect of increasing the value of b from 2 to 4 is to decrease the overall deposition velocity for 10 µm particles by about 30%. Varying the ratio of the viscous drag to the total drag between 0.25 and 0.45 exerts little effect on the deposition velocities for particles in the 1 – 10 µm size range. 2-8
Table 2-1. Parameters used in the Slinn (1982) model for estimating the deposition velocity over a bean crop. Parameter Description Equation used Value in Base Case Fraction of total interception by User-specified 1% F s small collectors such as vegetative hairs A s Characteristic width of small collectors such as vegetative hairs User-specified 10 -5 m (10 microns) Characteristic radius of large collectors such as grass blades, User-specified 10 -3 m (1 mm) A L stalks, needles, etc Unknown numerical factor used in User-specified 1 c Equation 2-18 and assumed to be near unity Numerical factor used to calculate User-specified 2 b particle rebound in Equation 2-19 Ratio of viscous to total drag User-specified 1/3 c v/c d within the canopy h Height of the canopy User-specified 1.18 meters Fraction of canopy equal to User-specified 20% F l characteristic Eddy size u * Friction velocity User-specified 0.25 m/s Roughness height User-specified or estimated from knowledge of z r, u r, 0.054 m z 0 h, and l Wind speed at reference height z r User-specified or estimated from u *, z 0, and d and 1.94 m/s u r Equation 2-9 or from u *, z r, u r, h, and l, and Equation 2-10 Wind speed at canopy height h Estimated from l and z 0 and Equation 2-12 or from u r, 0.81 m/s u h u *, h, and l and Equation 2-13 d Displacement height User-specified or estimated from h and F l and Equation 0.94 m 2-11 l Characteristic Eddy size at the top Estimated from F l and h 0.24 m γ of the canopy Parameter that describes the wind speed profile within the canopy expected to be between 2 and 5 User-specified or estimated from u *, u h, h, and d and Equation 2-20 or from c d, l, h, and α and Equation 2-21 3.8 Slinn (1982) suggests using γ=3. However, this assumption for γ is not consistent with Equation 2-20 The deposition velocity is sensitive to the assumed wind conditions. The roughness height, z 0 , and the displacement height, d, are mathematical tools used to fit the wind speed to a logarithmic profile such as in Equation 2-9; they are not directly measurable quantities. In general, z 0 varies from 10 -5 m for smooth ice to 10 m for a high-density urban area (Seinfeld and Pandis, 1999). Vegetative covers span the range between 0.01 m for cut lawn to 1 m for a tree-covered area. The displacement height is related to the canopy height, but can only be roughly estimated without field measurement of the wind profile above the canopy. Slinn (1982) makes the approximation that the displacement height is equal to 80% of the canopy height and that the sum of d and the characteristic Eddy size, l, is equal to the canopy height (i.e. l=0.2h). U * is also a “fitted” quantity and specifying its value requires some knowledge of the wind speed profile. Figure 2-6 shows that there can be significant deviations in v d when slightly different values for z 0 , u * , and l are assumed. Thus, without accurate data for these parameters, the deposition velocity may only be known to within a factor of about two or three. 2-9
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 and 24: Planetary Boundary Layer (PBL) F =
Page 25 and 26: C D u* = ur The overall drag c
Page 27: St a vg u g = cA L * Equation 2
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
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 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
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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