Life-Cycle Impact Assessment
The next step is life-cycle impact assessment (LCIA). In this step, the material numbers are converted from the inventory analysis into a manageable number of representative values. The LCA practitioner converts thousands of numbers from the LCI to a meaningful representation in three steps as follows: classification, characterisation/normalisation, and valuation.
Each of the thousands of inventory table data points is classified according to an environmental problem. These could include environmental issues such as resource depletion, energy depletion, global warming, photochemical oxidation, acidification, toxicity, ozone depletion, eutrophication, and many others (midpoint categories). Material from the inventory table may contribute to more than one category. It should be noted, in this context, that carbon- and water footprinting are essentially subsets of LCA, each with its own potential set of rules around setting boundaries and classifications. Various organisations promote their own set of classification categories including the methods such as ReCiPe, CML, Eco-indicator, TRACI, GLAM, and many others (Guinee, 2015). Each of the categories also has a weighting factor for characterisation as explained in the subsequent section.
Once all the materials have been classified into a category, each material is given a weighting factor depending on their relative impact to the category in question. Weighting factors are defined in terms of some other chemicals, e.g., global warming is given in terms of C02 equivalents; 1 kg of CH4 equals 25 kg С02еС| (IPCC GWPlOOa method). Weighting factors multiplied by the amount of material give the contribution of such a material to the final LCA scores. Summing all the contributions from each material in a category gives a final LCA score for that category.
It must be noted that values from characterisation can seem meaningless in isolation. However, they are more meaningful when used as a comparison to a similar product/process (or during an improvement assessment), or when the assessment is broken down to show the contributions of individual parts of the whole system, e.g., transport, manufacture, use, or disposal. In other words, the LCA result of a plastic bottle from company A (or production line X) is more understandable when compared to the product of company В (or production line Y).
Another way to make sense of the numbers from characterisation is when many LCAs have been performed and a comparison is made from the studies. This is termed normalisation. This involves comparing the size of a contribution against the total contribution to the problem over one year. For example, if a process is emitting one tonne of pollutant and the global number is one million tonnes per year, then the normalised value for the process is one-millionth of a year (10"6 years) or about 32 seconds.
The readers must take note that the information presented in this chapter has been overly simplified. In advanced studies, characterisation itself can be broken further into midpoint or endpoint categories as may be seen from an environmental or human health perspective, and areas of protection (human health, ecosystem quality, and natural resources). Impact assessment, in general, is the area of LCA that defines characterisation, and this is where it is constantly under methodological scrutiny. For more in-depth analysis of the topic, it is suggested that the readers find a specialised textbook on the topic such as Guinee (2015) or visit up-to-date websites that have more information, e.g., the UN Environment Programme's LCInitiative.
A last step in the quantification procedure in the LCA is the valuation step. This is the conversion of characterisation scores into a final single value. Each characterisation value gets a weighting, and all weighted values are summed to give a single score. While valuation and single scores are sometimes available, they are not common. Therefore, often, LCA practitioners leave results at a midpoint characterisation value (Figure 8.5).
To perform the steps in the LCIA phase, specialist LCA software are available, i.e., both open-source and proprietary software options are available. The important aspect of the software is the availability of databases on which to build new LCAs. Such databases are available from several sources, with some of them giving users tens of thousands of datasets.
Representative steps of the LCA from obtaining an inventory table, through classification, characterisation, and valuation.
The design of LCAs are such that they are to be questioned at each stage of the process; this is the role of the interpretation phase. It is particularly easy in the earlier stages to have numbers without much knowledge of what they mean. Due to an iterative nature of LCA, improving parts that are problematic during the interpretation phase (after each other stage) strengthens the confidence of the LCA results. The interpretation phase is also purposefully designed such that the practitioner is reminded to look back at what the exact scope of the study was and ensure the results meet the expectations of what should have been investigated.