Environmental Engineering Reference
In-Depth Information
6
0.15
0.10
5
4
0.05
3
0.00
2
-0.05
1
-0.10
0
-0.15
0
50
100
150
200
0
50
100
150
200
wind direction (deg)
wind direction (deg)
Fig. 3
Hourly wind speed and stability distributions against mean meteorological wind direction,
with corresponding histograms at Nordbysletta monitoring site
Nordbysletta is located north-east of Oslo in a rural, relatively flat environment
with average roughness length estimated to be 0.25 m. The road segment used in
the campaign is ~850 m long with four lanes orientated ~60° due north (in the N-NE
and S-SW sectors). Three stations measuring concentrations of NO
x
and one back-
ground station were located at different distances from the road. The measurement
height was 3.5 m. At station 2, there was also a meteorological mast measuring
hourly wind speed data, wind direction data, temperature and vertical temperature
difference between the heights of 10 and 2 m. In addition, hourly traffic counts and
average speeds of light and heavy duty vehicles separately were available. The traffic
flow is on average 36,000 vehicles/day, and the speed limit is 90 km/h
[3]
.
Distributions of wind speed and stability are presented in Fig.
3
. The mean meteo-
rological wind direction is parallel to the road with values 0° and 180°. Minimum
wind speed at 10 m height is fixed to 0.5 m/s. The histograms show that there are a
lot of low wind speed cases distributed evenly over the directions. Near neutral stability
prevails, but also the peak of very stable conditions is observed. The meteorological
conditions, with many cases of flows nearly parallel to the road, are rather demanding
for the purposes of dispersion modeling.
Computational Methods
The Gaussian fine line source model CAR-FMI used in this work is described, for
example in
[4]
. The model is based on the general solution of
[5]
. The current
version allows the use of separate emission data. The lowest wind speed in the
plume is restricted to 0.3 m/s.
