Chemistry Reference
In-Depth Information
(1)
If possible, allocation should be avoided by
expanding the system boundaries or disaggre-
gating the given process into different sub-
processes.
(2)
If it is not possible to avoid allocation, then the
allocation problem must be solved by using
system modelling based on physical causation,
which reflects the underlying physical relation-
ships among the functional units.
(3)
Where physical relationships cannot be estab-
lished, other relationships, including the eco-
nomic value of the functional outputs, can be
used.
• Photochemical oxidant formation (photochemical
smog)
• Human toxicity
• Aquatic toxicity
The definitions of these impacts are given in the
Appendix.
Characterisation
is a quantitative step to calculate
the total environmental impacts of the burdens esti-
mated in inventory analysis. This is a quantitative
phase of LCA and should be based on the scientific
findings on the relevant environmental impacts. In
the problem-oriented approach, the impacts are
calculated relative to a reference substance. For
instance, CO
2
is a reference gas for determining the
global warming potential of other related gases, such
as CH
4
and other VOCs. In general terms, impact
E
k
can be calculated by using Equation 5.2:
Further reading and real industrial examples on
allocation can be found in Refs 15, 19 and 20.
Impact assessment
J
The effects of the environmental burdens identified
in the Inventory Analysis phase are assessed and
characterised in the Impact Assessment phase. This
part of LCA is based on both quantitative and qual-
itative procedures to characterise and assess the
environmental impacts of a system. It consists of
four steps:
Â
E
=
ec
B
(5.2)
k
k j
,
j
j
=
1
where
ec
k,j
represents the relative contribution of
burden
B
j
to impact
E
k
, as defined by the problem-
oriented approach. The calculation procedure for
different impact categories is given in the Appendix.
A simple illustration of the calculation of global
warming can be found in Box 5.1.
Research on LCI assessment methods to calculate
impact categories is still ongoing [22]. It is recog-
nised that there is a relatively large uncertainty in
impact assessment associated with number and
type of impact categories considered, range of
burdens included within each category, parameters
used within the modelling of impacts and the model
used for each impact category [23]. To address some
of the problems related in particular to modelling of
impacts, research has been initiated to incorporate
multimedia fate modelling into LCA to calculate the
local and regional environmental impacts of prod-
ucts and activities. One such model is USES-LCA
(Uniform System for the Evaluation of Substances,
adapted for LCA) [24]. However, further work is
required in this area before fate modelling is adapted
fully and used routinely in LCA.
Normalisation
of impacts on the total emissions or
extractions in a certain area over a given period of
time also can be carried out within the Impact
Assessment phase. Some argue that because LCA is
global in its character, total world annual impacts
should be used as the basis for normalisation. Total
(1)
Classification.
(2)
Characterisation.
(3)
Normalisation.
(4)
Valuation.
Classification
is a qualitative step in which the
burdens are aggregated into a smaller number of
impact categories to indicate the potential impacts on
human and ecological health and on resource deple-
tion. The aggregation is done on the basis of poten-
tial impacts of the burdens, so that one burden can
be associated with a number of impacts; e.g. volatile
organic compounds (VOCs) contribute to both global
warming and ozone depletion. The approach used
most widely for classification of the impacts is known
as 'problem-oriented' [21], whereby the burdens are
aggregated according to their relative contributions
to the environmental effects that they may have. The
impacts most commonly considered in LCA are:
• Resource depletion
• Global warming
• Ozone depletion
• Acidification
• Eutrophication
