FIELD TESTING AND EVALUATION OF DUST DEPOSITION AND ...

value which was used up to the midpoint between the second and third measurement, and
so on.
6.2.3 Calculation of Horizontal Flux
The power law wind profile is appealing since analytical solutions exist for the
integral of a power law for wind with either an exponential or a Gaussian function for
dust concentration. For the exponential dust concentration case:
F dust =
C(z) u(z) dz =
∞
( Ae − Bz)
z
u ref
0
z ref
P
− P Γ( P +1)
dz = Au ref z ref
B ( P+1)
Equation 6-4
where Γ is the gamma function. Using a mathematical model that results in a converging
definite integral avoids any uncertainty about the upper limit of integration, z max . The
integral of a power law for wind, times a power law for dust concentration has an analytic
solution, but does not converge. For this study, the horizontal dust flux was also
calculated by trapezoidal rule numerical integration of Equation 6-1 using alternative
interpolation equations to model the time averaged wind speed and concentration as a
function of height. Variable step size (starting at ∆z = 0.1 m) was used to provide higher
resolution near the ground where both concentration and wind speed change rapidly with
height.
6.3 Results
The data were collected during two vehicle activity periods between 01:00 and
02:30 Mountain Daylight Time on September 26, 2001. The clear sky, nighttime, desert
conditions resulted in a stable atmosphere during the sampling period. Wind speed was
generally between 1 and 5 m s -1 , which was sufficient to move the dust cloud, and the
wind direction relative remained within 45° of perpendicular to the container array and
road. General meteorological data are summarized in Table 6-2. Table 6-3 gives the
wind speed and dust concentration mean and standard deviation.
Table 6-2 Meteorological data from station DPG08, approximately 1 km south of test site, for
September 26, 2002 01:00-03:00 MDT.
Average Range
Temperature 294 K 293 - 297 K
Relative Humidity 23% 20-26%
Barometric Pressure
866.54 mbar
24 hr- Precipitation 0
Wind at 10 m 3.0 m s -1 15 m s -1 gust
Wind Direction from True North 98-186°
6-4