Environmental Engineering Reference
In-Depth Information
Following the methodology of ISO 14040:2006, the LCIA includes the following
steps:
Step 1. Selection of environmental impact categories, impact category indicators, and
characterization models from the LCI (e.g., climate change, acidification, human
health).
Step 2. Assignment of life cycle inventory results to impact categories, also called
classification (e.g., the impact of carbon dioxide on climate change or in the
acidification of oceans).
Step 3. Calculation of category indicators, also known as
characterization
, using
conversion factors.
Step 4. Presentation of data after characterization.
Step 5. Optional elements of a LCIA: normalization, grouping, weighting, data quality
analysis.
According to ISO 14040, steps 1 through 4 are mandatory and step 5 is optional.
Step 1: selection of impacts
ISO 14044:2006 states that the selection of impact categories, category indicators, and
characterization models must be justified and consistent with the goal and scope of the LCA.
The selection of impact categories should be a reflection of the environmental issues related
to the product or system being studied and can be done according to two different schools of
thought:
1. Classical impact assessment methods, also known as problem-oriented methods or
midpoint methods.
2.
Damage oriented methods, or endpoint, methods.
For example, chlorofluorocarbons (CFCs) have been implicated in stratospheric ozone
depletion. Release of CFCs into the atmosphere is the
source
of a chain of environmental
events that produces ozone layer destruction (an impact category) that can be expressed by a
midpoint category indicator such as ozone depletion potential. However, even when strato-
spheric ozone depletion is a problem by itself, its impact on humans and ecosystems are of
larger concern and can be expressed with endpoint indicators such as number of species lost
or cases of human health impairment (Jolliet et al., 2004).
Step 2: classification
Once the category indicators are selected, the next step is to assign the results of the LCI to
the category indicators (e.g., kg of greenhouse gases emitted to the air). Figure 4.6 shows
the interrelationship between midpoints categories—see definitions of midpoint indicators
in Table 4.5—and endpoints categories for common impacts found in a food-production
systems.
Step 3: characterization
Characterization is the assessment of the magnitude of potential impacts of each inventory
flow into its corresponding environmental impact (Roy et al., 2009). Impact categories can
have global, regional, or local scales (Table 4.6). Impact characterization uses science-
based conversion factors, called
characterization factors
, to convert and combine the LCI
results into representative indicators of impacts on human and ecological health.
Characterization provides a way to directly compare the LCI results within each impact
