Page 104 - Materials Chemistry, Second Edition

100 5. Development and applicability of life cycle impact assessment methodologies

FIG. 5.3 Executions steps of life cycle assessment
impacts assessment. Inventory analysis
of an LCA

Classification Categorize inventory items

Confirm evaluation basis points

Characterization Choose measurement basis points

Describe by conversion model

Normalization Use quantization method

Valuation

subclasses are also separated from the broad categories of environmental impacts, when the
broad category of the impact on ecosystems consist of global warming, acidification, photo-
chemical smog, ozone depletion, water eutrophication, and so on (Du and Karoumi, 2014).
Different categories of environmental emission could make the same kind of environmental
impact. For example, the inducing factors of haze include PM2.5, SO 2 ,NO X , and so on, but
SO 2 could also cause acidification.
The environmental impact potential of the environmental emission factor is quantified by
characterization, which is the basis of related knowledge about physics, chemistry, biology,
and toxicology. The computational models of characterization consist of load model, equiv-
alent model, inherent chemical behavior model, overall exposure-effect model, and site
exposure-effect model. The equivalent model is the most commonly used model. In this
model, each impact type will be offered a specified matter as reference substance, called
the characteristic factor. The impact potential to one impact type of the other matter will
be measured by the characteristic factor. For example, the ability to cause the greenhouse ef-
fect of greenhouse gases will be expressed as CO 2 equivalents, where the ability to cause the
greenhouse effect of exhausting 1kg CH 4 is equivalent to the ability of exhausting 25kg CO 2 .
The final step is normalization. According to the contribution, different types of environ-
mental impact are weighted to evaluate integrated environmental impact (ISO, 2006c). There
are many environmental impact types to be investigated. The normalization is a necessary
step, which helps decision-makers make an overall consideration about every aspect of
environmental impact, avoiding decision mistakes caused by lack of knowledge.