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the product, aimed at covering and possibly aggregating indicator results
across impact categories.
• Data quality analysis serves to better understand the reliability of the
LCIA results better.

The use of models is necessary to derive the characterization factors. The appli-
cability of these factors depends on the accuracy, validity and characteristics of the
models used. For most LCA studies, no models are needed because existing impact
categories, indicators and characterization factors can be selected.
Models reflect the cause–effect chain, also called environmental mechanism or
impact pathway, by describing the relationship among the life-cycle inventory
results, indicators and, if possible, category endpoints or damage indicators. For
each impact category, the following procedure is proposed in ISO 14042 (2002):

1. Identification of the category endpoints
2. Definition of the indicator for given category endpoints
3. Identification of appropriate LCI results that can be assigned to the impact
category, taking into account the chosen indicator and identified category
endpoints
4. Identification of the model and the characterization factors

Figure 3.2 illustrates the relationship among the results of the life-cycle inventory
analysis, indicators and category endpoints for one impact category for the example
of acidification. It clearly shows where a model is needed. These items are explained
in detail in this chapter.

EXAMPLE
Life-cycle inventory results kg NO 2 , Pb, SO 2 , etc.

Impact
Acidification
Category
Inventory results assigned
to impact categories
NO 2 , SO 2 , etc.
Model
+
Proton release (H )
Category indicator
Environmental
relevance

Category endpoint(s) Forest, vegetation, etc.

FIGURE 3.2 The concept of indicators (ISO 14042, 2000) (available at www.afnor.fr).

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