Environmental Engineering Reference
In-Depth Information
Fig. 6
Main characteristics of the mixing zone concept
The additional width accounts for the initial horizontal dispersion imparted to
pollutants by the vehicle wake. Within the mixing zone, the mechanical turbulence
created by moving vehicles and the thermal turbulence created by hot vehicle
exhaust is assumed to be the dominant depressive mechanisms.
The chemical transformation is modeled by the so-called receptor-oriented discrete
parcel method. The model includes the basic reactions of nitrogen oxides, oxygen
and ozone, but the influence of other compounds is neglected. The influence of
plume dilution has been accounted for according to the receptor oriented Discrete
Parcel Method
[4]
, which is a modified version of the original method.
The CALINE4 requires relatively minimal input from the user. Input data are
traffic volume, emission factors, roadway geometry, wind speed and direction,
ambient air temperature, mixing height, atmospheric stability class and coordinate
of receptors.
Model Experiments and Results
By using CALINE4 dispersion model, hourly and 8-h average concentrations can
be obtained. The CO and NO
2
concentrations have been calculated at 100 m away
from the road axis for the Hungarian motorway network. NO
2
concentration is
shown in Fig.
7
for worst-case meteorology, where input is the combination of the
worst wind speed, wind direction, and stability class. The highest concentrations
occur around Budapest, which is explained by arterial roads structure in Hungary
and by urban sprawling.
