Page 261 - Materials Chemistry, Second Edition

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calculated for each process and pollutant, then the defined initial cut-off criteria are
applied. For processes and pollutant, respectively, the percentages and cut-off criteria
are represented graphically to visualize the data. The graphical presentations may
suggest redefining the respective cut-off criteria in order to obtain a manageable
number of processes that can be assessed in detail. In principle, this is an iterative
procedure to find the optimum. The decision-maker decides whether one or more
impact scores are to be considered and in which relation to each other. This means
also that dominance could be carried out with different cut-off criteria for different
impact scores, for instance, 5% for the human toxicity potential and 10% for the
acidification potential.
In the case of selection of processes, the processes to be assessed by site-specific
and site-dependent factors (generally obtained by project-related impact assessment
studies) and those to be assessed in a process-specific and/or region-dependent way
(generally by values published in the literature) must be determined.
In a next step, the most relevant pollutants and industrial processes (differentiated
in site-specific and site-dependent as well as in process-specific and/or region-
dependent ways) are determined. Qualitative arguments can also be used in this
decision and, in a sustainable perspective, social and economic aspects are important.
Therefore, it seems evident that, for instance, PCDD/Fs must be considered in a
case study on waste incineration due to their relevance for discussion in society,
although their percentage of the total impact score is less than the lowest selected
cut-off criterion (See Figure 6.13).
Finally, the identified predominant pollutants and regions must be assigned to
sites or regions. How far this is possible depends particularly on the information
available about the location of a specific process. Thus, it must be taken into account
that the site might be unknown; in this case, only the approximate global region can
be assigned, but not the specific site. The spatial scale of the pollutants depends on
their residence time in the respective medium. Many background processes whose
LCI data are normally taken from databases are broadly spatially distributed. Here
the question is to determine the most adequate size for a region; for example, in the
case of electricity production, the LCI data for the electricity mix of a country
generally are taken.
A problem that occurs in the assignment of sites is that often it is not the site
that most influences the environmental damages, but the emission height. This can
be concluded from the results for the site-dependent impact factors obtained in
Chapter 7. Therefore, instead of regions, a differentiation is made essentially accord-
ing to classes that have similar characteristics with regard to the emission situation
(determined by the geographic site and the stack height). However, in this method-
ology they are called regions because this term illustrates the idea behind spatial
differentiation much better.
Consistent with Expression 6.7, the world is the corresponding region for pol-
lutants that cause a global environmental impact like CO . In agreement with Expres-
2
sion 6.8, in the case of mobile processes, i.e., transports, it must be decided if the
environmental loads can really be assigned to one region only or must be differen-
tiated among two or more regions if the distance is long enough. The determined
processes assigned to sites and regions are the M processes and the chosen pollutants

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