Environmental Engineering Reference
In-Depth Information
on the diffusion and deposition of gasses and particulate matter. For this, ENVI-
met contains a plant physiologic model which calculates the stomata resistance
based on the local radiation, leaf surface temperature, the ratio of leaf- to ambient
air CO
2
-concentrations and water content. For the latter one the CFD-model is
coupled to a simplified soil model as well.
The model is applied within the framework of the Dutch Air Quality Innovation
Program (IPL). The ambition of the programme is to come up with a strategy to
improve local air quality in the vicinity of motorways and so called hot spots. One
of the seven braches of the project is the investigation, both by the means of in situ
measurements and by modelling, of the effect of line vegetation along a motorway.
In this framework, the model results have been compared to a first measurement
campaign which was executed before in the summer of 2006 along the A50 close
to the village of Vaassen, The Netherlands (Weijers et al., 2007).
2. Model Setup
In order to perform a validation study between the measurement campaign and the
ENVI-met model, a total area of 200 by 600 m and up to 50 m height has been
modelled. The whole domain is subdivided into non-overlapping elements,
121,688 in total, with a spatial resolution of 6 × 6 × 2 m with a vertical refinement
in the lowest five cells. Five measurements days have been modelled (only 3 for
PM). During these days the mean wind direction was mainly perpendicular to the
motor way, but varies between plus and minus 45°.
The traffic emission are modelled as line sources, one line per lane. The emission
rates are based on the local traffic counts by the Dutch Ministry of Transportation,
multiplied by the Dutch emission factors defined by the Ministry of Housing,
Spatial Planning and Environment.
3. Model Results
ENVI-met was capable of representing the measurement campaign quite well.
fine particles at 2 m height. These are the mean concentrations averaged over 5
days of measurements (three measurement days for PM) and normalized with the
value of the concentration just in front of the vegetation barrier. The plots show
both the modelled concentrations, full lines, and the measured mean values, dots
with error bars. The red dots and lines represent the measurements and model
results in the reference field, while the green dots and lines represent the measure-
ments and model results in front of and behind the vegetation. The green bar
indicates the location of the vegetation barrier and the red blocks at the bottom the
location of the traffic emissions.
