Page 253 - Materials Chemistry, Second Edition

4.5 Impact Categories, Impact Indicators and Characterisation Factors 237

should be used. The respective GWP values are listed in publications of the IPCC
and the corresponding updated (i.e. most recent) values should be used.
A prediction of temperature increase does not only depend on scientific princi-
ples but also on the development of GHG releases in the future and whether or
when suitable measures are taken and whether these measures will not be anni-
hilated by continuing economic growth. These trends can only be simulated with
appropriate scenarios whereby – in addition to the diverse atmospheric lifetimes of
the GHGs – a further time dependency is introduced.
In Table 4.10 the GWP 100 -values for most common GHGs are listed. 172) GWPs
of CFCs and some related chlorinated gases (e.g. HCFC-22, CCl ) are not listed
4
because besides having a usually very high heating effect they also exhibit com-
pensation effects, which cannot be precisely calculated. These can, in rare cases,
even result in a calculated cooling effect if aggregated. Should an inclusion of these
substances be necessary for a specific LCA these can easily be found in literature. 173)
Also GWP values with a shorter or longer time horizon (GWP 20 and GWP 500 )can
be found in the cited papers. In addition to the three most important GHGs (CO ,
2
CH ,N O), the highly persistent perfluorinated gases and partly hydrogenated
4 2
fluor-compounds used as freon substitutes must be considered. Compared to CO
2
they are only released in small quantities but show a GWP of up to 20 000-fold! This
is caused by a high IR absorbance and the persistence of these substances. The
perfluorinated substances are extremely hydrophobic and hence, are not washed
out by precipitations and do not react with OH radicals for other reasons. 174)
CO is the most important contribution to the overall GWP/fU in most LCA
2
studies. For a calculation of the GWP from the inventory only the CO that
2
originates from fossils (incineration of coal, oil, etc.) and minerals (calcination of
lime, production of cement) are considered, and therefore, have to be separately
assigned. CO from biological sources should also be assigned separately because
2
this amount is extracted from the atmosphere by photosynthesis relatively short
time ago and will again be released into the atmosphere by incineration or aerobic
degradation. Such emissions are often called CO -neutral although this is true only
2
over a sufficiently long time scale. The calculation of biogenic C-flow should not
be omitted because the investigation of a credible C-balance must be ensured and
documented transparently.
The greenhouse effect of the freons CFC-11 and CFC-12, which is not exactly
determinable in size due to side effects, is less known and has been addressed by
Ramanathan 175) shortly after the discovery of their ozone-depleting impact.

4.5.2.2.3 Characterisation The total GWP per fU is the sum of CO equivalents
2
which are calculated by a multiplication of GHG loads (m per fU) from the
i
172) IPCC/TEAP (2007), Velders and Madronich (2007), Kl¨ opffer and Meilinger (2001b), IPCC (1996,
2001) and WMO (1999).
173) IPCC/TEAP (2007); Table 2.6 in Velders and Madronich (2007).
174) Kl¨ opffer and Wagner (2007a,b).
175) Ramanathan (1975).