Page 208 - Materials Chemistry, Second Edition

192 4 Life Cycle Impact Assessment

indicator. Note: The common unit allows calculation of the (impact) category
indicator result.
In the example of the impact category climate change (see Section 4.3.2.1) this
translates as follows: The masses per fU assigned to this impact category from
the inventory are multiplied with a specific characterisation factor (GWP , e.g.
100
equals 1 for CO and 25 for CH ) and converted into (kg CO -equivalents). Thus
2 4 2
a common unit is obtained. With it, different GHGs can be added into an overall
(impact) category indicator value of the respective impact category (see Figure 4.2).
Characterisation models and characterisation factors are developed by specialised
sciences. The scientific basis of the more important impact categories in LCAs at
present are introduced in Section 4.5.
The calculation of category indicator results based on inventory data is automat-
ically accomplished by relevant software. This explains a widespread thoughtless
way of conducting the LCIA. ISO 14044 therefore requires that procedures
used for the calculations must be documented, including applied value choices
and assumptions. This demand is not trivial, because the basics are often
not kept in mind. It is also pointed out that the complexity of environmental
impact mechanisms (often not fully investigated) also cover spatial and tempo-
ral characteristics, for example the persistence of a substance in the environ-
ment 29) and dose-effect characteristics. It will usually be impossible to include
all these factors into the impact assessment; only if the complexity is adequately
addressed can the results be relevant and meaningful and overinterpretation can
be avoided.

4.3.3
Optional Elements of LCIA

4.3.3.1 Normalisation
Normalisation is defined according to ISO 14044 30) as the
… calculation of the magnitude of the category indicator results relative to some
reference information. The aim of the normalization is to understand better the
relative magnitude for each indicator result of the product system under study …
Normalisation means that category indicator results – thus the numerical results
of the characterisation – are divided by selected reference values.
As reference values national, regional (e.g. European Union and North America)
and international values (e.g. Organisation for Economic Co-operation and Develop-
ment, OECD) are used with respect to an approximate accordance with geographical
system boundaries. The principle and benefits of normalisation are illustrated in
the following three examples:

29) Kl¨ opffer and Wagner (2007a,b).
30) ISO 14044 206: 4.4.3.2.1