Page 200 - Materials Chemistry, Second Edition

186 R.K. Rosenbaum et al.

of a reference substance for the impact category which would lead to the same level
of impact (e.g. kg CO 2 -equivalents/kg of substance emitted for climate change).
In contrast, endpoint CFs are typically expressed in absolute units and the units are
relatively common between those LCIA methods that cover endpoint modelling:
Human health: [years] expressed as DALY (Disability-Adjusted Life Years). This
unit is based on a concept proposed by Murray and Lopez (1996) and used by the
World Health Organisation. It considers different severity contributions defined as
“Years of Life Lost per affected Person” YLL p [year/disease case] and “Years of
Life lived with a Disability per affected Person” YLD p [years/disease case]. These
statistical values are calculated on the basis of number and age of deaths (YLL) and
disabilities (YLD) for a given disease. This information can be combined into a
single indicator using disability weights for each type of disability to yield the
“Disability Adjusted Life Years per affected Person” DALY p [year/person].
2
3
Ecosystem quality or Natural environment:[m year] or [m year] expressed as
Potentially Disappeared Fraction (PDF). It can be interpreted as the time and area
(or volume) integrated increase in the disappeared fraction of species in an
ecosystem [dimensionless] per unit of midpoint impact indicator increase. It
essentially quantifies the fraction of all species present in an ecosystem that
potentially disappears (regardless whether due to death, reduced reproduction or
immigration) over a certain area or volume and during a certain length of time.
Different ecosystems have different numbers of species that can be affected by the
impact and it is necessary to correct for such differences when aggregating the
potentially disappeared fractions of species across the different impact categories at
endpoint (i.e. a PAF of 0.5 for 10 species represents 5 species potentially lost,
whereas the same PAF for 1000 species represents 500 species potentially lost).
Resource depletion and ecosystem services: Different approaches exist and since
there is still no common perception of what the area of protection for resources is
(Hauschild et al. 2013), there is also no consensus forming on how to model
damage in the form of resource depletion. Some proposals focus on the future costs
for extraction of the resource as a consequence of current depletion, and these
divide into costs in the form of energy or exergy use for future extraction (measured
in MJ) or monetary costs (measured in current currency like USD, Yen or Euro).

10.2.3.12 Uncertainties?

Uncertainties can be important in LCIA and contribute substantially to overall
uncertainty of an LCA result. For some impact categories, this contribution may be
much larger than that of the LCI. At the same time, it is also crucial to be aware that
large uncertainty is by no means a valid reason to exclude an impact category from
the assessment. One of the more uncertain impact categories is human toxicity and it
has to be capable of dealing with hundreds to thousands of different elementary
flows, which may differ by more than 20 orders of magnitude in their impact