FIELD TESTING AND EVALUATION OF DUST DEPOSITION AND ...

Height z (m)
14
12
10
8
6
T1_data
T2_data
T3_data
T1_ADE
T2_ADE
T3_ADE
4
2
0
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Normalized Concentration
a. u * = 0.3
Height z (m)
14
12
10
8
6
T1_data
T2_data
T3_data
T1_ADE
T2_ADE
T3_ADE
4
2
0
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Normalized Concentration
b. u * = 0.5
Figure 5-8. Concentration profiles measured at the three towers downwind of an unpaved road and
concentration profiles predicted by the ADE model for equivalent downwind distances a. for 32
passes with u * between 0.15 and 0.25 m/s and b. for 15 passes with u * between 0.45 and 0.55 m/s.
Tower distances from edge of road: T1 - 7 m, T2 – 50 m, T3 – 100 m. Modeled profiles are based on
neutral atmospheric conditions. Both measured and modeled concentration have been normalized to
the concentration at 1.26 m.
It is interesting that the Gaussian model used in the ISC3 better emulates the
concentration profiles observed in the experiment, especially since the gaussian plume
equations are actually approximate analytical solutions to the Atmospheric Diffusion
Equation. This is illustrated in Figure 5-9 where normalized concentrations at Towers 2
and 3 are plotted on the same graph as the predicted gaussian concentration profile. The
value of σ z in the ISC3 model is based only on atmospheric stability and downwind
distance. Thus, friction velocity is not represented. This is partly why experimental
conditions corresponding to low values of u * are better represented by the “moderate” to
“very” unstable curves. Higher values of u * correspond to “slight” to “moderate”
5-13