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L1644_C07.fm Page 282 Monday, October 20, 2003 12:10 PM

situation of Catalonia, after a minimum of between 40 and 50 ka, the population
density reaches a local maximum between 80 and 90 km. A look at Figure 7.6
explains this behavior: all rural regions are located around the agglomerated region
— especially the central cities in the rural regions, which are within a distance of
100 km of the agglomerated region.
For the rural districts of the rural regions, the population density is much below
2
the average of Catalonia (r = 190 persons/km at the radius r = 0), which is self-
explanatory in rural districts. Toward r = 100 km, the population density increases;
this explains the settlement structure of Catalonia. Statistically, a big city (central
city) is within a distance of 100 km of each rural district in a rural area. Another
look at Figure 7.6 underlines this reasoning.
From the curve for each class, it can be seen that the population density reaches
a similar value for all classes at a radius of 100 km. Therefore, it is statistically
justified to treat the long-range transport in an averaged manner (regional average)
for all considered districts and regions and to set the limit between short-range and
long-range modeling at this distance.

7.6.3 SHORT- AND LONG-RANGE EXPOSURE

The classes derived in the fate and exposure analysis are given combined class codes
in order to enable easy discovery of the desired impact indicator for the combined
classes. For example, the impact indicator for class III B describes the impact for a
central city in a rural region with annual wind speed conditions between 2 and 3
m/s. Moreover, the stack height is mentioned and the effect analysis method chosen.
For the short-range exposure, calculations are carried out for every combination
of pollutant, stack height and generic meteorological file. Concentration curves such
as those in Figure 7.7 are overlapped with the curves of radial population density
(Figure 7.7) for each generic class of population density and integrated over the
modeling area (see Expression 7.8). The integration over the modeling area is done
by summing up the products of concentration increment, population density and
area for all values lying in the chosen grid.
For the long-range exposure, the concentration increment is calculated for eight
grid cells of fictitious emission sites covering Catalonia, using the EcoSense software
(IER 1998). The runs are carried out for stack heights of 5, 100 and 200 m. As a
first step, the background population exposure is calculated (zero emission run). For
this purpose a “no emission” run is carried out for each of the eight grid cells. The
concentrations obtained are the background values for the respective grid cells.
Multiplying the background concentration and the population of each grid cell leads
to the background population exposure per grid cell. The results are then summed
up over all grid cells, which leads to the overall background population exposure
for each emission cell considered.
The next step is to carry out the calculations for all considered emission cells
and for all stack heights. The population exposure is calculated in the same way as
for the background population exposure. In order to obtain the long-range contribu-
tion due to an incremental emission of a pollutant, first the background population

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