FIELD TESTING AND EVALUATION OF DUST DEPOSITION AND ...

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volume, and dm ceil /dt is the mass per unit time passing through the ceiling of the control volume Because the road dust is usually the overwhelming source of dust, that is, dm road /dt >> dm ambin /dt + dm ceil /dt , the horizontal flux dm out /dt for these conditions is approximately: dm road /dt = dm out /dt which is the horizontal mass flux of dust from the road. Equation 4-19 4.1.3.1b Deposition at the floor and vertical flux of dust through the ceiling of the control volume downwind of the road The total loss of material diffusing vertically through the ceiling and depositing on the floor of the control volume to the left of the road may be calculated by first calculating the effective concentration at position x to the left of x 0 (i.e., the left edge of the road). We use the equation: V dC( x) dx = − C( x)[ V ∆z d + K] Equation 4-20 where, V is the wind speed that carries the dust through the control volume (CV), C(x) is the concentration of dust mass at position x in the CV, x is the horizontal position in the CV, increasing to the left, z is the vertical position in the CV, increasing from the floor to the ceiling, V d is the deposition velocity, and K is a coefficient having the dimensions of velocity. A solution to Equation 4-20 is: dmroad = Vd + K C( x) dt exp− x − x V∆z∆L V∆z o [ ] ( ) Equation 4-21 Multiplying C(x) by V d L (i.e., the deposition velocity times the unit length of the road) and integrating with respect to x from x = x 0 to x = gives: dm depos dt V = d dm dt ( V + K ) d road Equation 4-22 4-8
By making the approximation that dm ambout /dt - dm ambin /dt 0 and ignoring dm ceil /dt we may rewrite Equation 4-17 as: dmup dm dm road depos = − dt dt dt Equation 4-23 Watson (personal communication, 2000) stated that the condition dm ambout /dt - dm ambin /dt 0 was observed in the field for a distance x of about 200 meters in the absence of any intervening dust sources. 4.1.3.1c Ratio of vertical flux of road dust into the atmosphere to the horizontal flux of road dust The ratio of the mass per unit time emitted through the ceiling of the CV downwind of the road (dm up /dt) to the mass emitted from the road (dm road /dt) is called the “transportable fraction” and represents the fraction of emitted road dust that can be considered to be regionally transported. This fraction Φ is given in Equation 4-24. dmup dt Φ = = dm 1 − road dt V K ( V + K ) ( V + K ) d d = d Equation 4-24 The value of K was derived by using data of Porch and Gillette (1977) and (Gillette, 1974). Porch and Gillette (1977) provided data on fast-response concentrations of diffusing dust simultaneously taken with fluctuation vertical wind speeds at the same location. Analysis of the high-speed data showed that the aerosol flux could be expressed approximately as 0.04u * [C] where [C] is the mean mass concentration. Analysis of gradients of dust concentration in wind-eroding fields (Gillette, 1974) showed that the aerosol flux could be expressed as approximately 0.07u * [C]. The mean of the coefficients of [C] for these analyses gave a value of 0.06 u * which is the suggested value for K. Using Equation 4-24 with K equal to 0.06 u * , yields the “transportable fraction” of fugitive dust emitted from the road. Practical application of Equation 4-24 can use values of V d chosen to represent particle size and environmental conditions, for example, those of Slinn (1982). Values of u * are chosen by the user to represent the environmental conditions of interest. 4.1.3.2 Discussion The expression given in Equation 4-24 may explain part of why observed concentrations are smaller than that predicted by regional scale models that do not correct for the transportable fraction of emitted dust but rather use the entire amount of dust emitted by roads. However, there are limitations in applying this model to natural 4-9
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 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: oad. M is the mass of particles in
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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