Introduction to Life-Cycle Assessment and Decision Making Applied to Forest Biomaterials 171
Table 5.5Normalization factors based on a US citizen’s impact over the course of a year in
2008 (Ryberget al., 2014).
US normalization factors
reference year 2008
Impact category
Annual
(impact per year)
Per capita (impact
per person year)
Ecotoxicity – nonmetals (CTUe) 2.2E+ 10 7.6E+ 1
Ecotoxicity – metals (CTUe) 3.3E+ 12 1.1E+ 04
Carcinogens – nonmetals (CTUcanc.) 1.7E+ 03 5.5E− 06
Carcinogens – metals (CTUcanc.) 1.4E+ 04 4.5E− 05
Noncarcinogens – nonmetals (CTUnoncanc.) 1.1E+ 04 3.7E− 05
Noncarcinogens – metals (CTUcanc.) 3.1E+ 05 1.0E− 03
Global warming (kg CO 2 eq) 7.4E+ 12 2.4E+ 04
Ozone depletion (kg CFC-11 eq) 4.9E+ 07 1.6E− 01
Acidification (kg SO 2 eq) 2.8E+ 10 9.1E+ 01
Eutrophication (kg N eq) 6.6E+ 09 2.2E+ 01
Photochemical ozone formation (kg O 3 eq) 4.2E+ 11 1.4E+ 03
Respiratory effects (kg PM2.5 eq) 7.4E+ 09 2.4E+ 01
Fossil fuel depletion (MJ surplus) 5.3E+ 12 1.7E+ 04
option B are divided by scenario with the highest value for an individual impact. For
instance, if product A produced 20 kg eq. of CO 2 and option B produced 50 kg CO 2 eq.,
scenario A values would be divided by option B, 20 kg/50 kg. In a comparative study,
this method has some advantages as this goal is often to provide information that leads
to making a decision that will produce the lowest impacts. Since this goal is based on
deciding between one of multiple options, the scenarios can be normalized between
each other.
Weighting Weighting is a subjective methodology where the relative importance of
impact categories is determined. This can be useful in simplifying the results of an LCA
especially when there are trade-offs between scenarios. For instance, in the production
of a paper product two bleaching processes are used and compared in an LCA; however,
option A has lower impacts in three categories while option B has lower impacts in four
categories. It is often unclear how to compare GWP to acidification potential midpoint
indicators. Through weighting normalized midpoint indicators can provide further
insightsthatcanbeusefulindecisionmakingandcanbeusedinasingleenvironmental
score.
Weighting values are often determined by stakeholder groups involved in the project,
such as a company commissioning the LCA study. Alternatively, standardized weighting
values established in other studies can be used. One example of standardized weighting
values is the Eco-indicator 99 impact assessment method. For the Eco-indicator 99
method (Ministry of Housing, 2000), a panel of 365 people was asked to rank the
importance of ecosystems health, resource use, and human health. The results from
this Swiss LCA interest group panel indicated that the human health and ecosystems
