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Spatial differentiation in LCA impact assessment

10. Example of the application of site -dependent impact assessment

• 10.1 Normalisation
• 10.2 Interpretation

Examples in Chapters 4-9 have demonstrated the application of the EDIP2003 site-generic and site-dependent characterisation factors on the same example. The example which is introduced in Section 1.6 concerns an LCA-based comparison of the use of zinc and the use of plastic (polyethylene) as material for a supporting block (a structural element) in the seat of an office chair.

Figure 10.1 summarises the difference between the site-generic and the site-dependent impacts for the different impact categories.

As seen from Figure 10.1, the inclusion of spatial differentiation at the level of country of emission influences the size of the impact potential to a larger or minor extent for all impact categories. Sometimes the site-dependent impacts are higher than the site-generic impacts, and sometimes they are lower, but the dominance of the zinc component over the plastic component is rather stable. Sometimes it is strengthened a bit (human toxicity via air), sometimes it is weakened a little (aquatic eutrophication) but only for two of the impact categories does site-dependent characterisation reverse the dominance of the zinc component. This is the case for the categories acidification and ozone impact on human health, where the elimination of part of the spatial variation in the dispersion patterns and sensitivity of the exposed environment means that the impact from the plastic component becomes larger than the impact from the zinc component. As stated in the ozone example in Section 7.9, the ozone impact on human health from the plastic component still comprises a significant potential for spatial variation, and therefore no conclusion can be drawn for this impact category without extending the site-dependent characterisation to comprise additional key processes.

Figure 10.1 Site-generic and site-dependent impact potentials for acidification, terrestrial eutrophication, photochemical ozone impacts on vegetation and human health, aquatic eutrophication, human health via air exposure and chronic ecotoxicity in water and soil from the two product systems. For the site-dependent impacts, the site-dependent characterisation factors have only been applied for the key processes as described in the respective chapters.

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10.1 Normalisation

In order to further investigate the importance of the findings described above, the site-dependent impacts calculated throughout the example are normalised in Table 10.1 using the relevant site-dependent EDIP2003 normalisation references for the different impact categories (site-dependent normalisation references are not available for the ecotoxicity categories).

The normalised site-dependent impact profile is shown in Figure 10.2. It is clear from the figure that compared to the background load of society, the different impact potentials have roughly the same size across the impact categories, except for the ozone impact to human health for the plastic component which is about twice the size of the other normalised impact potentials and the human toxicity impact via air which is lower than the others.

10.2 Interpretation

The potential spatial variation in the characterisation is large for many of the impact categories as revealed by the standard deviation on the site-generic characterisation factors throughout the example. In the example, spatially determined differences in sensitivity are considered relevant to the decisions that shall be based on the results of the LCA. Therefore, the spatial variation can be seen as an uncertainty on the conclusion. This uncertainty is so large, that based on the site-generic impact assessment, it is not possible to conclude dominance for one of the two supportive blocks for any of the investigated impact categories.

Table 10.1. Normalised site-dependent impact scores for the zinc and plastic components

Figure 10.2 Normalised impact potentials for the two product systems. Except for the ozone impact on human health, the major spatial variation in dispersion and exposure has been eliminated from the impacts.

A site-dependent characterisation removes the major part of this uncertainty for all impacts for the zinc component and for all impacts except photochemical ozone impact on human health for the plastic component. Compared to the site-generic characterisation, the dominance is reversed for two of the impacts – acidification and ozone impact on human health.

The normalised site-dependent impact potentials in Figure 10.2 show a trade-off where the zinc component is superior for acidification and ozone impact on human health while the plastic component has the lowest impact in the rest of the catgories. A weighting is needed to decide which alternative is preferable from an environmental perspective. If the ozone impact on human health turns out to be decisive, the site-dependent characterisation must be performed for an additional part of the processes in the plastic component's product system.

The weighting goes beyond the scope of this Guideline but it should be noted that in order to use the EDIP97 default weighting factors (based on political reduction targets), the two subcategories for photochemical ozone formation must be aggregated into one photochemical ozone formation impact potential. According to the EDIP97 methodology this is done by taking the average of the normalised impact potentials for the sub categories. The same holds true for the sub categories on eutrophication.

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Version 1.0 january 2006, © Danish Environmental Protection Agency