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5 Life Cycle Assessment of Chemical Products and Processes
• Human toxicity
It is important to note that a single flow can potentially contribute to more than
one of the impact categories chosen.
5.5.3 Step 3: Characterization
In the characterization step, elementary material and energy flows are multiplied by
a characterization factor for each of their classified impact categories. This results
in the calculation of impacts and allows the different flows to be compared to one
another with a common unit. Scientifically based characterization factors are used
within each available impact assessment method. They are often calculated using an
effect-based comparison with a reference substance.
The calculation of the characterization factors is different for each impact
category (and sometimes also among different impact assessment methods), and
a dose-effect relationship is used to define each. For a midpoint impact category i,
the impact (I i ) can be calculated across all material and energy flows (f j ) by using
the corresponding characterization factors (CF i,j ) as:
I i =
j
CF i,j × f j
(5.3)
• I i : impact within impact category i
• f j : material or energy flow j (from LCI)
• CF i,j : characterization factor (impact assessment method specific) for the conversion of material or energy flow f j into impact equivalents of the impact category i
For the midpoint impact category of climate change, for example, Eq. 5.3 would
be applied with the characterization factor for global warming potential (GWP) (see
Eq. 5.7 for details):
• I climate change =
j CF GWP,j × f j
Characterization factors can also be derived to translate impacts from midpoints to endpoints. Within the ReCiPe method, for example, midpoints are set
to contribute to three endpoint areas of protection: human health (expressed in
units of disability-adjusted life years (DALY)), ecosystems (expressed in units of
biodiversity loss), and resource availability (no harmonized unit set). The method
provides users with midpoint-to-endpoint characterization factors that can be used
in the same way to calculate damages to these three endpoints.
5 Life Cycle Assessment of Chemical Products and Processes
• Human toxicity
It is important to note that a single flow can potentially contribute to more than
one of the impact categories chosen.
5.5.3 Step 3: Characterization
In the characterization step, elementary material and energy flows are multiplied by
a characterization factor for each of their classified impact categories. This results
in the calculation of impacts and allows the different flows to be compared to one
another with a common unit. Scientifically based characterization factors are used
within each available impact assessment method. They are often calculated using an
effect-based comparison with a reference substance.
The calculation of the characterization factors is different for each impact
category (and sometimes also among different impact assessment methods), and
a dose-effect relationship is used to define each. For a midpoint impact category i,
the impact (I i ) can be calculated across all material and energy flows (f j ) by using
the corresponding characterization factors (CF i,j ) as:
I i =
j
CF i,j × f j
(5.3)
• I i : impact within impact category i
• f j : material or energy flow j (from LCI)
• CF i,j : characterization factor (impact assessment method specific) for the conversion of material or energy flow f j into impact equivalents of the impact category i
For the midpoint impact category of climate change, for example, Eq. 5.3 would
be applied with the characterization factor for global warming potential (GWP) (see
Eq. 5.7 for details):
• I climate change =
j CF GWP,j × f j
Characterization factors can also be derived to translate impacts from midpoints to endpoints. Within the ReCiPe method, for example, midpoints are set
to contribute to three endpoint areas of protection: human health (expressed in
units of disability-adjusted life years (DALY)), ecosystems (expressed in units of
biodiversity loss), and resource availability (no harmonized unit set). The method
provides users with midpoint-to-endpoint characterization factors that can be used
in the same way to calculate damages to these three endpoints.