## 6 Discussion
### Merging Natural Soil CO\({}_{2}\) Flux and GPPs' CO\({}_{2}\) Emissions  
The different components comprising the CO\({}_{2}\) budget for emissions in the AVGA are in the order of abundance: soil diffuse emissions, GPPs, and focused emissions (gas vents, thermal pools, and Hg mine infrastructures). All of the total collected data reported in Table 7 are visualized in the bar diagram shown in Figure 8, where the different single components and their sum are illustrated. The total soil CO\({}_{2}\) flux is subdivided into the background flux values (calculated by means of data statistics) coinciding with the biological population A of Figure 4 and in the deep CO\({}_{2}\) populations B and C of Figure 4 coinciding with the CO\({}_{2}\) naturally formed in thermometamorphic aureole of the volcano magma chamber intrusion and rising from deeper magmatic mantle sources. The total CO\({}_{2}\) emitted in the AVGA is estimated as 17,934 t/d (as shown by the right bar of Figure 8), of which diffuse deep CO\({}_{2}\) is 11,038 t/d, where the 262 t/d of focused emissions must be added to this value. The total deep CO\({}_{2}\) reaches 11,300 t/d. The CO\({}_{2}\) emissions of the six GPPs of Bagnore and Piancastagnaio fields sum to 1418 t/d, which represents 7.9% of the CO\({}_{2}\) emitted in the atmosphere in the AVGA. Another important focus concerns the analysis of the high CO\({}_{2}\) flux areas. As previously stated, these areas coincide with the Bagnore (area B in Figure 5) and Piancastagnaio (area C in Figure 5) geothermal fields and with the greenfield areas unaffected by geothermal operations of Bagni San Filippo (area A in Figure 5) and Paglia (area D in Figure 5). Figure 9 shows the emissions in the different high soil flux areas expressed as t/d. Similar emissions are observed in different areas and separated into the background (biological), deep, GPPs' emissions, and focused emissions. Because of the different areal extent of the high emission areas, a better way to analyze data is to normalize emissions for areas expressed as t/d km\({}^{2}\). \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Fossil-Fueled Power Plants**} & \multirow{2}{*}{**CO\({}_{2}\) g/kWh (2017)**} & \multicolumn{2}{c}{**Percentage of Fossil-Fuel Electricity Production in 2017**} \\ \hline Coal & 870 & 15.6 \\ Natural gas & 368.3 & 67.2 \\ Derived gas & 1498.4 & 1.2 \\ Petroleum & 548.9 & 5.5 \\ Others * & 133.3 & 10.5 \\ \hline \hline \end{tabular}  
* other solid and gaseous fuels including biomethane.  
\end{table} 
Table 6: CO\({}_{2}\) emission factors from fossil-fueled power plants in Italy [62]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Geothermal Area**} & **Year** & **CO\({}_{2}\) g/kWh** & **Reference** \\ \hline Larderello (Italy) & 2018 & 343 & Calculated based on ARPAT data \\ Italian geothermal fields (average) & 2014 & 321 & [63] \\ Italian geothermal fields (average) & 2015 & 343 & [63] \\ Italian geothermal fields (average) & 2016 & 311 & [63] \\ Iceland & 2018 & 26 & [64] \\ Iceland & 2012 & 34 & [65] \\ Indonesia & 2013 & 62.9 & [66] \\ USA & 2003 & 91 & [67] \\ USA & 2010 & 25.7 & [68] \\ California & 2014 & 107 & [65] \\ California, the geysers & 2013 & 45 & [65] \\ California, Coso & 2013 & 245 & [65] \\ New Zealand & 2012 & 104 & [65] \\ Turkey & 2014 & 1050 & [65] \\ Global & 2001 & 122 & [52] \\ \hline \hline \end{tabular}  
\end{table} 
Table 5: CO\({}_{2}\) emission factors from GPPs around the world. Figure 10 highlights first that a very similar normalized emission occurs ranging from 103-115 t/d km\({}^{2}\) in the four areas. These data point to the general observation that the CO\({}_{2}\) flux from deep sources is homogeneous in the AVGA. This observed behavior is most probably linked to the mechanisms of natural generation of CO\({}_{2}\) that several researchers [16] claim are because of the thermal processes in the thermometamorphic contact aureole of the Mt.