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directions is assumed to be valid. The height of the mixing layer is calculated
according to VDI 3782/1, which is a German guideline on dispersion modeling. The
uncertainties introduced are therefore considered to be small. The surface roughness
is chosen as one value for the whole of Catalonia as a rural value, which is assumed
to be a good estimate for the general settlement structure of Catalonia.
Classes according to the population density are formed. It is argued that the
statistical basis is good enough to calculate the radial population density and that
it is valid to use an interval of 10 km for the annuli considered because the biggest
municipality in Catalonia has a smaller surface. However, reducing the resolution
outside Catalonia to the district level increases the uncertainties. It is assumed that
this is a reasonable procedure because it only concerns a limited number of
adjacent districts to Catalonia and, with respect to working loads, this is a feasible
way.

7.7.7.4 Consequence and Effect Analysis

One of the most important sources of uncertainties relates to the dose–response and
exposure–response functions of pollutants further described in Chapter 4. These
functions determine the consequence and effect analysis. Therefore, uncertainties
due to these functions directly apply to the endpoint-related indicators or damage
estimates (physical impacts such as cancer cases, as well as YLD, YOLL, DALY
and external environmental costs). If one wants to avoid these uncertainties, the
impact indicators can be applied as “pressure on human health.” However, in order
to take into account the differences in the toxicity of the pollutants and sensitivity
to human health, dose–response and exposure–response must be considered. For
instance, the EcoSense database offers a variety of dose–response functions that can
be chosen according to the value preferences of the user and which show huge
relative differences. More functions can be obtained from other public health or
environmental authorities.
YLD, YOLL, DALY and external environmental costs are determined by sub-
jective judgment that directly influences the outcome. In order to increase the
transparency and reduce the subjective influence by the methodology developer, this
work offers several options. For uncertainties about YLD, YOLL and DALY values
for several pollutants, see Hofstetter (1998). For more information on uncertainties
in the evaluation of external environmental costs, see the EC (2000).

7.8 QUESTIONS AND EXERCISES

1. Why is a differentiation between near (<100 km) and far (>100 km)
necessary for the impact assessment in the case of air emissions?
2. How is the fate analysis carried out for the presented site-dependent
approach?
3. Explain how the exposure analysis is performed for the presented site-
dependent approach.

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