Civil Engineering Reference
In-Depth Information
Weighting is not a scientifi cally based operation, but it relies upon the
opinion and attitude of experts towards different environmental effects. on
the other hand, the relationship between midpoint category indicators and
LCi results is easily established through appropriate, scientifi cally based,
characterization models. That is why the 'midpoints' approach is often used
to quantify the results in the early stage in the cause and effect chain to limit
the uncertainties (Mateus and Bragança, 2011). The most representative
example of this type of approach is CML methodology, developed at the
institute of Environmental Sciences (CML) of the Faculty of Science, Leiden
University in The netherlands. Their choice of impact categories (only
baseline) is shown in Table 3.5 (Guinée et al., 2002).
Characterization model
The link between the LCi results (extraction of resources, emissions and
waste), and the category indicator is normally given by clear modeling
algorithms (iSo, 2003). These modeling algorithms are called characterization
models. Many characterization models for different impact categories have
been developed. in the following, characterization models proposed by CML
methodology (Guinée et al., 2002) are briefl y presented.
∑ Climate change: the characterization model of the iPCC (intergovernmental
Panel on Climate Change). The iPCC provides characterization factors,
global warming potentials (GWPs), for three different time horizons: 20,
100 and 500 years in terms of Co
2
equivalents. The indicator result is
estimated by calculating the product of the amount of emitted greenhouse
gas per functional unit of produced material (
m
i
) and the GWP given in
Co
2
-equivalents for each gas (
GWP
i
) . Finally, the contribution to the
indicator result from each gas is summarized:
Σ
i
[3.1]
Climate change =
GW
GW
GW
Pm
Pm
Pm
i
Pm
i
i
i
∑ Stratospheric ozone depletion: the characterization model of the WMo
(World Meteorological organization). This model provides characterization
factors, stratospheric ozone depletion potentials (oDPs) for a steady state
in terms of CFC-11 equivalents:
Σ
i
[3.2]
Stratospheric ozone depletion =
ODP
×
m
i
ODP
i
i
×
m
i
i
The indicator result is expressed in kg of the reference substance, CFC-
11 equivalent.
ODP
i
is the steady state ozone depletion potential for
substance
i
, while
m
i
(kg) is the quantity of substance
i
emitted.
Similarly, the category indicators (midpoints) are proposed for other impact
categories, and together with other relevant data, shown in Table 3.6. The
