Page 200 - Materials Chemistry, Second Edition

184 4 Life Cycle Impact Assessment

An aggregation to critical volumes starts with the ‘critical volume’ (c.V.) of an
emission i per functional unit (fU) into an environmental medium j according to
Equation 4.1:
Emission ∕functional unit emitted into medium j (mass)
c.V. = limit value for i in medium j (mass∕volume) (volume) (4.1)
i

j: air, water and soil (and/or groundwater).
The emission per fU refers to the entire life cycle, therefore corresponds to the
mass aggregation of all unit processes corresponding to the individually released
substances i in the inventory. As such, only direct releases into the same medium
j are aggregated. A further distribution in the sense of multimedia models (see
Section 4.5.3.2.4) is not made. As most limit values have the dimension mass per
volume, the aggregation has the dimension volume and is called critical volume.A
definition of the limit values as mass per mass, for instance in the soil compartment,
would lead to a ‘critical mass’, which however is not common. 9)
The c.V. of one substance i has a clear meaning: it represents the volume of pure
i
air, pure water or pure soil, which is needed to dilute a released pollutant quantity
c.V. /fU in order to just obtain the threshold value concentration. Here, particularly
i
very high values can occur for the medium air: A released mass of 1 kg fU −1 of a
substance i with a threshold value of 1 μgm −3 results in:
3
9
c.V. = 10 m ≡ 1km 3
i
For an aggregation of several emitted substances this visual evidence is lost,
since all compounds occupy the same virtual volume together. With an aggregation
for each compartment j the sum of c.V. of all individual emissions i is formed for
which both the data of the inventory and limit values are present (Equation 4.2):
c.V. = ∑ c.V. (4.2)
j i,j
i
As an example air pollutants of a non-specified packaging are considered here
(Table 4.1). The fU is the filling, packing and the transport of 1000 l of fruit juice.

4.2.1
Interpretation
Since existing limit values determine the size of the c.V., those air pollutants
with the lowest limit values specified in Table 4.1 dominate the sum value. In
regulations the lowest limits can be found for substances damaging human health
in low concentrations. Limits that encompass the damage to ecological systems as
a whole do not exist. Thus in the above example the aggregated value is dominated
by the c.V. for SO and NO . The Hydrocarbons (CH) are ranked as less toxic
x
2
(higher limit value) and are almost negligible for the final result. As no limit value
is specified for CO , it is not considered at all.
2
9) And give an association to the atomic bomb.