## 2 Methods
### LCA Methodology  
Life cycle assessment (LCA) is a methodology that is used to evaluate the environmental impact of a product over its entire life cycle. This LCA study considers a system through its life cycle from cradle to grave. The life cycle of a product system includes the manufacturing phase (extraction of raw materials, handling, and processing), operational phase (the normal and intended use of the product), and the disposal phase (the end of the product until landfill disposal) [19].  
In common, the major focus of utilizing LCA methodology is on reducing the environmental impact of specific products under consideration for more sustainable solutions through decision-making process [20]. A full LCA requires significant effort and expertise, although according to UNE-EN ISO 14040:2006 standard [21], performing an LCA should at least be performed through four main interrelated steps. Those steps are definition of the goal and scope, developing the life cycle inventory (LCI), carrying out the life cycle impact assessment (LCIA), to finally interpreting the results.  
The LCA of this study is based on the impact assessment method ReCiPe and global warming potential (GWP), extracted from the database Ecoinvent [22]. ReCiPe indicator was indicated by the Joint Research Commission of European Union [23] as the best method for the European context in comparison with EPS2000, Eco-indicator 99, and IMPACT2002+. The ReCiPe indicator, a method used to assess the environmental impact, is based on an update version of CML and Eco-indicator 99 [19]. The primary objective of the ReCiPe method is to transform the long list of life cycle inventory results into a limited number of indicator scores. These indicator scores express the relative severity on an environmental impact category. In ReCiPe indicators are determined at two levels, eighteen midpoint indicators, and three endpoint indicators. Midpoint indicators focus on single environmental interventions at the level of a cause-effect chain between emissions and the endpoint level. Endpoint indicators show the environmental impact on three higher damage levels: effect on human health, biodiversity, and resource scarcity [24]. Converting midpoints to endpoints simplifies the interpretation of the LCA results (Figure 3).  
The IPCC GWP indicator is used for characterization at midpoint level, and only this indicator was selected as representative for all midpoint model currently used in LCA studies according to the Joint Research Commission of European [26]. The IPCC GWP is an indicator based on the ratio of the radiative damage force of the greenhouse gases. In order to measure GWP, the gas must have a long atmospheric lifetime, which means that the gas lasts long enough in the atmosphere to mix and spread through it. This given time used by GWP depends on if it is desired to predict the emissions long-term effects (GWP 100a) or their short-term effects (GWP 20a), where the values of the GWP are measured in kgCO2-eq [27].  
The assessment of each impact category according to each indicator is given in Equation (1):  
\[IMP_{j}\ =\ \sum_{k}d_{k,j}.LCI_{k} \tag{1}\]  
where \(IMP_{j}\) is the \(j\) impact category, \(d_{k,j}\) is the coefficient of damage (extracted from database Ecoinvent) associated with the component \(k\) and impact \(j\) and, finally, the \(LCI_{k}\) is the life cycle inventory LCI entry (i.e., kg of paraffin) [28].