## 3 Life Cycle Assessment Methodology
### Goal and Scope Definition  
This phase is data-free and question-oriented and not quantitative as an overall methodology. Goal and scope explanations are provided by ISO 14040. The goal should define \"the willful application of the analysis, the motivations to develop the analysis, the willful audience of the analysis and if the obtained results should be used in comparative statements revealed to the public\". Then, it is necessary to explain the reason for the conducted analysis. The scope, instead, should define what is investigated in the analysis and how this analysis is going to be carried out.  
In addition to satisfying the above questions, the system boundaries of the analyzed system and functional unit are defined in this phase. System boundaries separate the technosphere from the cesosphere and border all processes considered in the life cycle analysis. Among the mentioned areas, the technosphere contains all analyzed and considered processes while the cesosphere is related to the environment. The interaction between the cesosphere and the technosphere is described by elementary flows (emissions and resources). On the other hand, flows inside the technosphere and between processes are called process flows or economy flows (valuable products or unwanted wastes) [63] From these considerations, it is evident that elementary flows are the inputs and outputs of the system boundaries, while process flows are inside the system boundaries, as shown in Figure 3. To be more precise, ISO 14040 says that elementary flows are in the input and output of \"the analyzed system without previous or succeeding human transformations\" (ISO 14040, ISO 14044).  
Figure 2: Stages of a life cycle assessment analysis according to the ISO standards (ISO 14040, 2009 [61]; ISO 14044, 2006). Phase 1: Goal and scope definition; Phase 2: Inventory analysis; Phase 3: Impact assessment; Phase 4: Interpretation [modified after [PERSON] [62]].  
According to the selected system boundaries, different life cycle assessments can be developed: cradle to grave: a complete life cycle assessment considering the resource extraction (cradle), use phase, and disposal phase (grave); cradle to gate: a not complete life cycle assessment considering the resource extraction (cradle) but not the use and disposal phases; cradle-to-cradle: a particular cradle-to-grave analysis for which the disposal phase is a recycling process to produce new, identical, or different products; gate to gate: a not complete life cycle assessment regarding only one process of the overall chain; well-to-wheel: a particular life cycle assessment used for the transportation of fuels and vehicles in order to evaluate energy consumptions and efficiencies and emission impacts.  
Another element that is defined in the goal and scope definition phase is the functional unit. The functional unit quantifies the performances of a system or service and it is the reference to relate all inputs and outputs, allowing a comparison of different case studies. Also, the functional unit establishes if the analyzed functions (defined as in Section 2.2) are evaluated jointly or separately, and it is defined by the scope of the study.