Page 92 - Materials Chemistry, Second Edition

74 LIFE CYCLE ASSESSMENT HANDBOOK

2. Provide a readily understandable, complete, and consistent pre-
sentation of the results of an LCA study, in accordance with the
goal and scope of the study.

It is important to remember that LCA is best used as an iterative approach. It
is especially important to determine that if the results of the impact assessment
or the underlying inventory data are incomplete or unacceptable for drawing
conclusions and making recommendations, then the previous steps must be
repeated until the results can support the original goals of the study. Also, LCA
as a decision support tool should be used in conjunction with other decision
criteria, such as cost and performance, to make a well-balanced decision.

4.3 Principles and Framework of LCIA

According to ISO, the assessment of the magnitude of potential impacts on the
environment is called characterization. The CF is applied to convert the results
of a life cycle inventory assigned to a given impact category to the common unit
of that category indicator. It is a numerical value expressing the relationship
between an environmental intervention (e.g. 1 mg of lead emitted into air) and
an environmental indicator. This latter is generally calculated by a characteriza-
tion model that expresses a simplified mathematical representation of physical,
chemical and biological processes occurring along the cause-effect chain.
The collection of individual characterization models or methods (each
addressing their separate impact category) is referred to as an "LCIA method-
ology" (e.g. referring to the CML 2002 method or the IMPACT 2002+ method).
"Method" refers, therefore, to the individual characterisation model while
"methodology" is the collection of methods.
According to ISO 14044, the indicator of an impact category can be cho-
sen anywhere along the stressor-impact chain (i.e. the impact pathway) which
links inventory data to impacts which are directly related to an AoP, i.e. Human
Health, Natural Environment, and Natural Resources. Characterization can be,
and is, conducted by some practitioners at the endpoint. However, more com-
monly models apply CFs at the midpoint level to reflect impact calculations
somewhere along (but before the end of) the impact pathway (Jolliet, Miiller-
Wenk et al. 2004). A trade-off between midpoint and endpoint modeling exists.
On one hand, midpoint indicators are removed from observable or tangible
impacts, making it harder for the public to relate to the indicator results. On
the other hand modeling to an endpoint introduces additional uncertainty as
the location specific data become less certain and less available. That is, it is
easier for people to grasp the significance of crop loss due to acid rain rather
than an indicator that shows a potential increase in acidification, measured in
hydrogen-ion equivalents.
Midpoints are defined where a common mechanism for a variety of sub-
stances within that specific impact category exists. Impacts that occur at the
global level, such as global warming and ozone depletion, are more amenable