## 2 Objectives and Methodology  
The research question underlying this study is as follows: Is the large-scale use of EVs environmentally more sustainable than the use of ICVs?  
To assess whether EVs will be more or less environmentally sustainable, it is necessary to take into account all the impacts (direct or indirect) that may occur on the overall system, including all of its life cycle. This implies a macro view (of the whole and its complex and comprehensive interactions), and not just the micro dimension (analyzing only a small, limited, simplified, and circumscribed aspect).  
Environmental sustainability can be assessed/measured using various parameters such as ecological footprint or CO\({}_{2}\) emissions. In this work, CO\({}_{2}\) emissions were defined as the indicator of the level of environmental sustainability. This choice was based on the fact that CO\({}_{2}\) emissions are a quantity that is easily converted from electrical energy and is frequently used in this area [27] and can translate the impact of new infrastructures that are needed [28].  
To answer the research question, the following objectives were defined:  
1. Identify sources of CO\({}_{2}\) emissions and create a framework to facilitate the calculation of emissions associated with large-scale EV use, from a macro perspective;
2. Calculate CO\({}_{2}\) emissions resulting from large-scale EV use, from a macro perspective using the developed framework;
3. Compare with the emissions of an ICV.  
From a methodological point of view, and in order to achieve the intended objectives, the following steps were followed:  
1. To create the framework: 1. A non-systematic bibliographical search was carried out, focusing on articles published in scientific journals on the ways of integrating EVs into the EES (the B-on and Google Scholar platforms were used). 2. From this research, the main characteristics and needs of each of the EV integration modes were identified. 3. In each mode, the main aspects that contribute to CO\({}_{2}\) emissions were identified. 4. The identified information was systematized, and the framework was developed.
2. To calculate CO\({}_{2}\) emissions: 1. Based on the developed framework, studies were identified that calculate partial emissions due to EVs (micro view). 2. Calculations were made to standardize the various studies and/or conversion calculations of identified impacts into CO\({}_{2}\) emissions.  
* CO2 emissions were calculated from a macro (global) perspective, taking into account the structure of the framework developed and the various modes of EV integration.
* The value of emissions obtained was compared with emissions from an ICV.  
As described, the present study is based on other published studies that present partial and fragmented (micro-) analyses, using their results to build a macro and comprehensive view that allows for estimating the global impact of EVs on CO2 emissions.  
The main contributions of this work are the following:  
(i) The creation of a framework identifying the main contributions to CO2 emissions resulting from large-scale EV integration. This is a relevant contribution to future research that aims to analyze in a more complete and realistic way the impacts on the environmental sustainability of EVs.  
(ii) The calculation of estimated CO2 emissions from a macro perspective, enabling a more adjusted assessment of the impact of large-scale EVs and a more realistic comparison with ICV emissions.