## 2 Materials and Methods
### Life Cycle Assessment  
The life cycle assessment method, standardized by ISO standards and ILCD handbook [42; 43; 57], assesses the potential environmental burdens of human-dominated processes and systems in a \"cradle to grave\" perspective, from the extraction of raw materials to the disposal of generated waste, through distribution and use. The results provided different kinds of impact categories, including emissions and resource consumption [58]. It is performed by following a four-step procedure:  
1. Goal and scope definition: in this phase, the objective, the functional unit (FU) and the burdens of the investigated case study are clearly defined. In this work, the LCA method is used to support and integrate the results of the performed i-Tree Canopy study. The chosen FU is the assessment of the impact categories affected by the ecological functions delivered by the current and potential tree cover within the boundaries of the Metropolitan City of Naples. \begin{table}
\begin{tabular}{l l c c} \hline \hline \multicolumn{4}{c}{**Annual Air Pollution Removal Benefits**} \\ \hline \multirow{2}{*}{**Item**} & \multirow{2}{*}{**Description**} & **Removal Rate** & **Monetary Value** \\  & & **(g/m\({}^{2}\)/yr)** & **(USD/t/yr)** \\ \hline CO & Carbon monoxide & 0.03 & 192.29 \\ NO\({}_{2}\) & Nitrogen dioxide & 0.22 & 63.03 \\ O\({}_{3}\) & Ozone removed & 7.37 & 549.10 \\  & Particulate matter & & \\ PM\({}_{10}\) & greater than 2.5 & 1.47 & 889.02 \\  & microns and less than & 10 microns & \\ PM\({}_{2.5}\) & Particulate matter less & & \\ SO\({}_{2}\) &
\begin{tabular}{l} Plan 2.5 microns \\ Sulphur dioxide \\ \end{tabular} & 0.05 & 38,529.50 \\ \hline \multicolumn{4}{c}{**Annual Hydrological Benefits**} \\ \hline \multirow{2}{*}{**Item**} & \multirow{2}{*}{**Description**} & **Tree effects (L/m\({}^{2}\)/yr)** & **Monetary Value** \\  & & **(USD/m\({}^{3}\)/yr)** \\ \hline AVRO & Avoided runoff & 0.60 & 2.60 \\ E & Evaporation & 14.94 & \\ I & Interception & 14.95 & \\ T & Transpiration & 107.41 & \\ PE & Potential evaporation & 545.19 & \\ PET & Potential & 488.30 & \\  & evapotranspiration & & \\ \hline \multicolumn{4}{c}{**Carbon Benefits**} \\ \hline \multirow{2}{*}{**Description**} & \multirow{2}{*}{**Carbon Rate (t/ha/yr)**} & **Monetary Value (USD/t)** \\ \hline Carbon sequestered annually & 30.60 & \\ Carbon stored in trees’ lifetime & 768.48 & 187.99 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Removal rate and monetary value of benefits of tree coverage estimated by i-Tree Canopy. 2. Inventory analysis: LCA analyses are performed by means of specific inventories listing all relevant input and output flows enabling processes and/ or subprocesses within the investigated case studies. Inventories are usually dimensioned considering the chosen FU, and include primary data (directly collected), secondary data (from scientific literature, databases, etc. ), and tertiary data (calculations and assumptions). In this work, data for the used inventories come from the i-Tree Canopy tool, listing the pollution and hydrological benefits of tree cover. Hence, the inventory is built considering the annual mass of uptaken flows: particulate <2.5 \(\upmu\)m; particulate >2.5 \(\upmu\)m and <10 \(\upmu\)m; sulphur dioxide; ozone; nitrogen dioxide; carbon monoxide and carbon dioxide; and the annual avoided water runoff in the assessed area in the present and future potential scenarios. 3. Impact assessment: this step translates the input and output flows in the inventories into potential impacts in different categories by means of specific characterization factors related to distinct impact methods.