Introduction
The general structure of an LCIA consists of some mandatory elements that convert the results of the LCI phase into appropriate indicators that can be used directly or as a starting point for subsequent optional LCIA assessments. The elements that constitute the "mandatory" phase are:
- the selection of environmental effects to be considered in addition to the environmental indicators that represent them;
- the allocation of LCI phase results to the selected environmental effects (classification)
- the calculation of category indicators (characterization)
An important aspect also concerns the evaluation criteria to be adopted, which connect these numbers to the corresponding value judgments on the greater or lesser severity of the impact. All of this occurs in the second phase of the LCIA, called “optional” and composed of additional elements:
- comparison of calculated environmental indicators with reference values (normalization)
- comparison of the importance of individual environmental effects (weighting)
Mandatory Phase - Selection & Allocation
The first operation to be carried out in LCIA is the choice of environmental effects (or impact categories) on which the analysis will be based. Some parameters constraining the choice may include the presence of reference regulations (e.g., EN15804, GHG Protocol, etc.) or product category rules (PCR, PSR, RCP, etc.).
Subsequently, we move to the classification phase, which operationally consists of organizing the inventory results, i.e., the values of all gaseous, liquid, and solid emissions generated directly or indirectly by the processes under consideration, distributing them into the various impact categories. However, the problem may not be easily solved as the same substance constituting an emission may contribute to multiple impact categories, causing chain effects that are difficult to interpret. Methane (CH4), for example, contributes to both the "global warming" and "ozone layer depletion" impact categories, or nitrogen oxides (NOx) which contribute to both the "photochemical formation" and "human toxicity" categories.
It is also important to clarify that while these categories refer to known effects, these must be considered (for now) only as “potential” effects. This is not only due to the uncertainty of the correlation resulting from the limits of scientific knowledge, but also because there is no claim to make a precise determination of environmental effects at the specific site under examination and at the exact time of the survey. This first phase is therefore of a general nature as it will simply lead to a quantitative connection of a production process to one or more impact categories. The aggregation of inventory results is not intended to provide absolute value judgments on environmental effects but allows for at most relative judgments, such as determining which of two or more production processes results in less resource consumption or a lower impact resulting from environmental releases (Potential impact).
Mandatory Phase - Characterization
After classifying the different impacts generated by processes, the characterization method allows for determining in a homogeneous and quantitative way the contribution of individual emissions. This makes it possible to express quantitatively, in a suitable unit of measurement, the contribution that the process under consideration provides to each category. In other words, it allows determining the values of category indicators that were previously defined for each individual effect considered. Put even more simply, each elementary substance identified and sorted into various impact categories is multiplied by its respective characterization factor (unit emission factor specific to each impact category), thereby obtaining the total impact of the various categories. Ultimately, the impact is represented by numerical values obtained by processing the results of the LCI with grouping and classification operations: its link to the “effect” lies in the fact that it is a potential cause. In this sense, the term “impact” should not be overemphasized when it is confused with the effect it can cause.
Optional Phase - Normalization & Weighting
The results from the characterization phase can be further processed to produce synthetic indices for an overall evaluation of the system under consideration. There are various normalization methods, each referring to special parameters that allow for the aggregation of results from different impact categories. The resulting environmental profiles are therefore synthetic and particularly suitable for comparing different production systems. However, the fact that normalization parameters are linked to artificial considerations and often questionable ones makes the normalization operation too risky, leading to reducing the entire environmental profile to a single reference parameter.
Normalization methods to be published in the next in-depth article belong to the MAUT (Multi-Attribute Utility Theory Decision Analysis) category and provide the possibility of choosing between different considerations by using a hierarchical scale of objectives that can be of top-down (identifying global aspects) or bottom-up (identifying specific aspects) (Jacaz et al, 1997).
