224
Air Pollution and Turbulence: Modeling and Applications
An application and validation of SPRAY performances, within RMS modeling
system, in experiments carried out in real complex terrain was worked out on the
TRACT (TRAnsport of air pollutants over complex terrain) fi eld campaign, performed in the Rhine valley, in southern Germany, during September 1992 (Fiedler,
1989; Zimmermann, 1995). Among many other measurements, TRACT included a
tracer release and the related concentration measurements (at ground level and aloft).
The main objectives of RMS simulations (Carvalho et al. 2002) were to verify its
capability to accurately simulate the 3-D transport and diffusion of a passive pollutant in a complex orography. In fact, the TRACT area is a rather complex region
characterized by the presence of valleys (such as the Rhine Valley) and mountains
(like the Black Forest, the Vosges, and the Swabian Alps).
RAMS simulations were performed using three nested grids, from a 16 km
(grid 1) up to a 4 km (grid 2) and 1 km (grid 3) horizontal resolution, and SPRAY
was run on all the grids. The tracer emission, near the ground level (source at 8 m)
lasted 3 h.
The model system correctly reproduced the general behavior of the plume (that
was divided into several tracer puffs), the temporal and spatial distribution of the
concentration, and the location of the concentration maxima during the 12 h of
observations. Also, the aloft simulated concentration values compared well with data
measured by aircraft.
This simulation work allowed demonstrating the feasibility of the complete simulation of a dispersion process (wind fi eld reconstruction, generation of the turbulence
fi eld, and reconstruction of the concentration fi eld) in complex terrain. This is of
fundamental importance for the air pollution problem and for the assessment of the
environmental impact.
As an example of the simulation results, Figure 8.2 shows the computed particle
positions (representing the tracer position), plotted over the 10 m wind fi eld, at different hours: 06, 08, 12, and 16 UTC on September 16, from top-left to bottom-right.
The more the time passed, the larger was the area involved and, consequently, a
different computational grid had to be consider. It can clearly be seen that, at the
beginning, the plume is very narrow and follows the wind direction along the Rhine
valley, as shown at 06 UTC (grid 3). Approximately 2 h after starting the emission,
the plume, though exhibiting a defi nite principal nucleus, also shows some puffs that
travel in different directions. At 08 UTC, the separation from the main plume clearly
appears (grid 2). Later the plume appears as a very large cloud and, at 12 and 16
UTC (grid 1), it clearly splits into two parts, one part remains close to the emission
source, and the other part moves toward southwest. It is worth mentioning that the
clouds’ position shown in all these fi gures correctly reproduced the observed plume
trajectory.
8.8.3 SINGLE SOURCES AND LINEAR EMISSIONS: IMPACT ASSESSMENT
IN COMPLEX TERRAIN
LSDM are advanced tools that in the last decade are pushing their ways through the
impact assessment framework. Lagrangian models offer a much better description of
the atmospheric physical processes with respect to simplifi ed models, but still demand
© 2010 by Taylor and Francis Group, LLC
Air Pollution and Turbulence: Modeling and Applications
An application and validation of SPRAY performances, within RMS modeling
system, in experiments carried out in real complex terrain was worked out on the
TRACT (TRAnsport of air pollutants over complex terrain) fi eld campaign, performed in the Rhine valley, in southern Germany, during September 1992 (Fiedler,
1989; Zimmermann, 1995). Among many other measurements, TRACT included a
tracer release and the related concentration measurements (at ground level and aloft).
The main objectives of RMS simulations (Carvalho et al. 2002) were to verify its
capability to accurately simulate the 3-D transport and diffusion of a passive pollutant in a complex orography. In fact, the TRACT area is a rather complex region
characterized by the presence of valleys (such as the Rhine Valley) and mountains
(like the Black Forest, the Vosges, and the Swabian Alps).
RAMS simulations were performed using three nested grids, from a 16 km
(grid 1) up to a 4 km (grid 2) and 1 km (grid 3) horizontal resolution, and SPRAY
was run on all the grids. The tracer emission, near the ground level (source at 8 m)
lasted 3 h.
The model system correctly reproduced the general behavior of the plume (that
was divided into several tracer puffs), the temporal and spatial distribution of the
concentration, and the location of the concentration maxima during the 12 h of
observations. Also, the aloft simulated concentration values compared well with data
measured by aircraft.
This simulation work allowed demonstrating the feasibility of the complete simulation of a dispersion process (wind fi eld reconstruction, generation of the turbulence
fi eld, and reconstruction of the concentration fi eld) in complex terrain. This is of
fundamental importance for the air pollution problem and for the assessment of the
environmental impact.
As an example of the simulation results, Figure 8.2 shows the computed particle
positions (representing the tracer position), plotted over the 10 m wind fi eld, at different hours: 06, 08, 12, and 16 UTC on September 16, from top-left to bottom-right.
The more the time passed, the larger was the area involved and, consequently, a
different computational grid had to be consider. It can clearly be seen that, at the
beginning, the plume is very narrow and follows the wind direction along the Rhine
valley, as shown at 06 UTC (grid 3). Approximately 2 h after starting the emission,
the plume, though exhibiting a defi nite principal nucleus, also shows some puffs that
travel in different directions. At 08 UTC, the separation from the main plume clearly
appears (grid 2). Later the plume appears as a very large cloud and, at 12 and 16
UTC (grid 1), it clearly splits into two parts, one part remains close to the emission
source, and the other part moves toward southwest. It is worth mentioning that the
clouds’ position shown in all these fi gures correctly reproduced the observed plume
trajectory.
8.8.3 SINGLE SOURCES AND LINEAR EMISSIONS: IMPACT ASSESSMENT
IN COMPLEX TERRAIN
LSDM are advanced tools that in the last decade are pushing their ways through the
impact assessment framework. Lagrangian models offer a much better description of
the atmospheric physical processes with respect to simplifi ed models, but still demand
© 2010 by Taylor and Francis Group, LLC