FIELD TESTING AND EVALUATION OF DUST DEPOSITION AND ...

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polycarbonate surfaces and those calculated for similar conditions according to Equation 3-3 and Equation 2-25. The difference between measured and predicted deposition velocities is quite large, ranging from one order of magnitude for large particles to two orders of magnitude for small particles. This difference is expected to be manifested in the overall deposition velocity (I.e. considering both r b and r a ) since the resistance to transport through the surface layer r a is very small compared to r b . That is, under the atmospheric conditions of Ft. Bliss, the deposition velocity is controlled almost entirely by the transport through the quasi-laminar sublayer. 100 Deposition Velocity (cm/s) 10 1 0.1 Vd=1/rb calculated Ft Bliss Expon. (Ft Bliss) 0.01 0 1 2 3 4 5 6 7 8 9 10 11 Aerodynamic Dp (microns) Figure 3-9. Measured deposition velocities on polycarbonate substrates and deposition velocities calculated based on the boundary layer resistance r b only vs. particle aerodynamic diameter. The average u * for the sample periods represented by the measured data and used for the theoretical prediction was 0.35 m/s. There is a subtle point that explains some of the differences between the measured and modeled deposition velocities. The measured values in this study represent deposition to a surrogate surface (artificial plant or flat substrate). It is likely that the density of the vegetation in the canopy, characterized perhaps by the fraction of ground area covered by plants should enter in the calculation of overall deposition to the canopy. That is, the surrogate surfaces used in this study may adequately simulate the removal of particles by individual vegetative elements, but do not account for the density of those elements. Some work in this area has been done by Raupach and Leys (1999), though testing of their hypotheses against data is not complete. 3.4 Conclusions An important point, directly relevant to this WESTAR project as a whole, is that the quantification of the deposition velocity is not a straightforward matter. Most models, including the ones discussed in (Chapter 2) are only tested against limited data sets, most notably those of Chamberlain (1967). One reason for this is that direct measurement of deposition velocities is quite difficult, and each of the available techniques has some significant shortcomings as noted by Dabberdt et al. (1993). Though use of surrogate surfaces for deposition is a common approach (e.g. Wu and Davidson ,1992; Etyemezian et al., 1999), it also suffers from shortcomings. Most notably, the surrogate surface is a 3-14
single element that is intended to induce similar transfer of material (momentum, particles, gases, etc) as an entire canopy. While there have been recent novel approaches that attempt to measure deposition in-situ (e.g. Gillies et al., 2001), at present there remain substantial uncertainties in the true value of deposition velocities. The solution to the difficulty of quantifying deposition is outside the scope of the present study. We note simply that values of v d calculated by any of the methods described in Chapter 2 may be erroneous in some cases by a factor of two or more, based on the input parameters alone. The results of this portion of the study, which utilized surrogate surfaces for deposition, indicate that measured deposition velocities are difficult to relate to theoretical formulation. This is illustrative of the ongoing challenge in reconciling data with theory in the field of dry deposition. 3-15
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: are deposition from a horizontally
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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