Page 190 - Materials Chemistry, Second Edition

176 R.K. Rosenbaum et al.

Further details on the selection of impact categories, category indicators and
characterisation models can be found in Rosenbaum (2017) and Hauschild and
Huijbregts (2015).

10.2.2 Classification

In this step, the elementary flows of the LCI are assigned to the impact categories to
which they contribute; for example an emission of CO 2 into air is assigned to
climate change or the consumption of water to the water use impact category,
respectively. This is not without difficulty because some of the emitted substances
can have multiple impacts in two modes:

• In parallel: a substance has several simultaneous impacts, such as SO 2 which
causes acidification and is toxic to humans when inhaled.
• In series: a substance has an adverse effect which itself becomes the cause of
something else, such as SO 2 which causes acidification, which then may
mobilise heavy metals in soil which are toxic to humans and ecosystems.
This step requires considerable understanding and expert knowledge of envi-
ronmental impacts and is therefore typically being handled automatically by LCA
software (using expert-based, pre-programmed classification tables) and not a task
that the LCA practitioner needs to undertake.

10.2.3 Characterisation

In this step, all elementary flows in the LCI are assessed according to the degree to
which they contribute to an impact. To this end, all elementary flows E, classified
within a specific impact category c (representing an environmental issue of con-
cern), are multiplied by their respective characterisation factor CF and summed over
all relevant interventions i (emissions or resource extractions) resulting in an impact
score IS for the environmental impact category (expressed in a specific unit equal
for all elementary flows within the same impact category):

X
IS c ¼ ð CF i E i Þ ð10:1Þ
i
For each impact category, the indicator results are summed to determine the
overall results for the category. In the following sections, the general principles of
how CFs are calculated and interpreted will be discussed. In order to provide a
better understanding of what CFs in each impact category represent and how they
are derived, Sects. 10.6–10.16 will, for each impact category, explain the