Page 45 - Materials Chemistry, Second Edition

26 LIFE CYCLE ASSESSMENT HANDBOOK

category c. This formula is the operational formula for characterization. With
a table of characterization factors specified, it makes clear that:

• LCIA builds on the results of LCI (as is clear from the term ra s);
• Characterization converts the results of LCI into a common metric
(as is clear from the multiplication by CF);
• Characterization aggregates the converted LCI results (as is clear
from the summation symbol).

The result from characterization is a list of numbers, for instance a score for
climate change, a score for toxicity, etc. ISO refers to such numbers as "category
indicator results/' but most LCA practitioners prefer names like "score/ 7
sometimes expanded with the name of the impact (as in "toxicity score"). The
complete list is known by names such as "LCIA profile," "characterization
table," etc.
After this sketch of the principle of characterization, let us have a look at the
more formal ISO point of view. Impact assessment in ISO is structured into a
number of steps:

• Selection of impact categories, category indicators and character-
ization models;
• Classification;
• Characterization;
• Normalization;
• Grouping;
• Weighting;
• Data quality analysis.

Although characterization is just one of the steps of impact assessment,
the former term is often used as a pars-pro-toto for the latter term. Indeed,
in discussing the principle of characterization above, we have touched upon
the steps of selecting categories, indicators, and models and characterization.
These are mandatory steps for ISO. The step of classification is mandatory
as well, but few LCA studies report it. ISO defines it as the "assignment of
LCI results to the selected impact categories." Its purpose is to clearly show
which emissions and extractions are treated under which impact category, but
it involves no numerical conversion into a common metric, as is the case for
characterization.
Normalization refers to calculating "the magnitude of the category indi-
cator results relative to some reference information." It is an optional step
for ISO, and indeed, many LCIA studies stop at the characterization. The
reference information is in most cases that total impact in a certain region in a
certain time period, e.g., in the country of decision in one year. Normalization
helps "to understand better the relative magnitude for each indicator result."
Without normalization, the indicator results are in quite different units, e.g.,
kg C0 2 -equivalent for climate change and MJ primary energy for fossil energy