Page 298 - Materials Chemistry, Second Edition

L1644_C07.fm Page 270 Monday, October 20, 2003 12:10 PM

DD = E ◊ M ◊ I (7.6)
i i i
where
DD is the incremental damage caused (damage) due to the exposure to one
i
pollutant being emitted at the emission situation i.
E is the effect factor (damage/persons.(mg/m ) yr) representing the severity of the
3
.
impact due to one pollutant.
M is the mass of one pollutant (kg) being emitted at the emission situation i.
I is the incremental population exposure per mass of one pollutant emitted at the
i
3
emission situation i (persons.(mg/m ).yr/kg).
Expression 7.5 can be divided into two integrals accounting for the short-range
dispersion and the long-range transport to the outer boundary of the modeling area R:

I is the short-range contribution to the incremental receptor exposure per
i,near
mass of one pollutant emitted at the emission situation i (per-
3
sons.(mg/m ).yr/kg).
I is the long-range contribution to the incremental receptor exposure per
i,far
mass of one pollutant emitted at the emission situation i (per-
3
sons.(mg/m ).yr/kg).
The reason for this procedure is that the concentration increment is usually
highest within the first kilometers around the stack. Therefore, the impact indicator
is very sensitive to the receptor density close to the stack. The population density
can vary strongly within only a few kilometers. Consider, for example, that the
population density often rapidly decreases from a big city to the countryside; there-
fore, the population exposure is subject to drastic changes within a few kilometers
as well. The long-range contribution, however, only depends on the average receptor
density of the region to which the pollutants are transported and is not particularly
subject to changes on a local scale; the concentration increment is small due to
dilution on transport and the concentration does not change very much with the
distance. Long-range contributions are known and have been well studied for pol-
lutants like SO and NO (due to their importance for acidification in regions far
2 x
away from the emission source). Strong differences for the long-range exposure are
likely to appear between densely inhabited areas such as western and middle Europe
and scarcely inhabited regions such as Scandinavia or, in the U.S., the East Coast
and the less populated Rocky Mountains. Therefore, as a good approximation,
country averages for I seem to be appropriate.
i,far
A major problem with deriving I is the fact that Dc (r,j) depends very much
i,near i
on the meteorological conditions, especially the wind direction, which can vary
significantly within a few kilometers for the different emission sites. It is therefore
desirable to eliminate j in order to simplify Expression 7.5. Nigge (2000) assumes
that Dc (r, j) and r (r, j) are not correlated and that the population density is
i i
independent of the angle j if the emission sites considered in each class are spread
over a large area. In this way, no direction is preferable for the spatial variation of

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