Page 297 - Materials Chemistry, Second Edition

L1644_C07.fm Page 269 Monday, October 20, 2003 12:10 PM

Generally speaking, the integration of Expression 7.5 should be carried out over
the entire planet. Because most of the pollutants (even in the air compartment) do
not disperse over the entire planet due to their residence time and dispersion char-
acteristics in the environment, and because the calculation effort should be kept
appropriate, R is chosen so that most of I is covered by the area. Another limitation
i
is the spatial range of the models chosen, which often does not allow the calculations
to be extended over a certain limit. The source characteristics influence the choice
of R as well. The higher the stack in the case of emissions to air, the further the
pollutant is transported and therefore the greater R must be chosen.
The idea of the methodology further developed and applied in this study is to
define classes of emission situations i statistically, the impact of which differs
significantly from class to class but for which the deviation of impact between the
emission situations covered by each class is small. The overall number of classes
should be kept small to enable easy handling.
On the one hand, neglect of the spatial distribution around the emission point,
I, of the receptor density, r(r,j), is the main reason for the discordance between the
potential impact results and the actual impacts. To be precise, this means, for
example, that in conventional LCIA potentials the impact is the same for an air
pollutant over the ocean as for one in a big city. On the other hand, the corresponding
dispersion conditions in the respective medium and the resulting concentration
increment, Dc (r,j), are relevant for the occurrence of damages. In order to relate
i
these main factors for the estimation of environmental damages in a process-chain
perspective, the present method proposes to form representative classes of receptor
density and dispersion conditions. This classification must be based on statistical
reasoning. For each class, receptor incremental exposures per mass of pollutant,
DRE, must be calculated.
In a next step, the receptor incremental exposures per mass of pollutant DRE
can be converted into damage estimates through an effect analysis based on
dose–response and exposure–response functions and, if desired by the decision-
maker, by the application of a weighting scheme to express different types of impacts
in the way of an aggregated damage.

7.4 GENERIC CLASSES FOR HUMAN HEALTH EFFECTS

For the case of human toxicity impacts of airborne emissions, the receptors are the
persons of a population and the release, as the target compartment is air. Thus, r m
eff r,
corresponds to the population density and the receptor incremental expo-
sures, DRE nm , are then called population incremental exposures to airborne pollut-
pr i,,
3
ants DPE, expressed in units of (persons mg/m ·yr). PE is also called pressure on
human health (Nigge 2000).
Many laws and regulations with respect to emission limitation and pollution
prevention exist for pollutants emitted into and solely transported by the air, so this
study is confined to air as the only release and target compartment. Considering
only human beings as receptors, for one pollutant Expression 7.4 can then be
simplified to:

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