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3 Life-Cycle Impact

Assessment

3.1 INTRODUCTION

The life-cycle inventory offers product-related environmental information consisting
basically of a quantified list of environmental loads (raw material consumption, air
and water emissions, wastes, etc.) that give the amount of pollutants to be assigned
to the product. However, the environmental damage associated with them is not yet
known.
Let us consider, for example, well-known air pollutants such as sulfur dioxide,
SO , nitrogen dioxide, NO , and hydrogen chloride, HCl, that generate an environ-
2
2
mental impact known as acid rain. The capacity of these pollutants to acidify the
+
atmosphere can be measured by the potential to generate H protons, so the acid
concentration could be multiplied by a corresponding factor to obtain a global value
+
of H protons equivalent. In this way an environmental impact category has been
measured based on inventory data. The same occurs with air emissions: carbon
dioxide, methane, nitrogen oxides, halocarbons, etc. contribute to Earth’s global
warming and cause the well-known greenhouse effect, measured in CO equivalents.
2
Thus a new type of impact category, global warming potential, is introduced from
inventory data.
Thus, the life-cycle impact assessment (LCIA) is introduced as the third step of
life-cycle assessment (LCA), described in ISO 14042 (2002) and further outlined in
ISO/TR 14047 (2002). The purpose of LCIA is to assess a product system’s life-
cycle inventory (LCI) to understand its environmental significance better. Thus, LCIA
provides information for interpretation — the final step of the LCA methodology.
Jointly with other LCA steps, the LCIA step provides a wide perspective of
environmental and resource issues for product systems by assigning life-cycle inven-
tory results to impact categories. For each impact category, impact potentials are
selected and category indicator results are calculated. The collection of these results
defines the LCIA profile of the product system, which provides information on the
environmental relevance of resource use and emissions associated with it. In the
same way as LCA as a whole, LCIA builds up a relative approach based on the
functional unit.
On the other hand, to compare the potentials for different impacts, it is necessary
to evaluate the seriousness of the impact categories relative to one another. This can
be expressed by a set of weighting factors — one factor per impact category within
each of the main category groups. The weighted impact potential, WP(j), can be
calculated by multiplying the normalized impact potential or resource consumption,
NP(j), by the weighting factor, WF(j), associated with the impact category.

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