## 2 Material and Methods  
In the most recent studies, the ancient carbon dioxide emissions have needed to be virtually reconstructed using the indirect method to evaluate emissions 'within the area', based on the amount of boric acid collected in each mining site around the Larderello area. The Tyrrenian margin of Italy is known to be affected by a large CO\({}_{2}\) diffuse soil emission ([PERSON] et al., 2017), linked to its geodynamical setting that gives rise to mantle upwelling, crustal thinning and subsequent extension and normal faulting. All of these characteristics are well highlighted and correlated in a recent paper by [PERSON] et al. (2021)([PERSON] et al., 2021). Larderello, one of the world's rarest superheated, steam-dominated systems, is located in central-western Tuscany, a Tyrrenian region dominated by high heat flow, widespread hydrothermal features, and a large flux of deep CO\({}_{2}\)([PERSON] et al., 2017). The site was already known in Etruscan times due to its natural surface manifestations: thermal springs, steaming ground, hot pools, geysers, and fumaroles all related to the geothermal system at depth. The upper reservoir of the Larderello geothermal field is composed of sedimentary rocks, carbonates, dolomites and anhydrides at shallow depth (from 300 m below ground level), while the second reservoir is hosted in metamorphic rocks such as phyllites, mica schists, schists and gneiss to a depth of 3500 m below ground level and other varying depths within the field. On the basis of \(\delta^{13}\)C and \({}^{3}\)He, isotopic study on wells in Larderello [PERSON] et al. (2005)([PERSON] et al., 2021) concludes that CO\({}_{2}\) (>90%) is mainly of crustal origin, related to the large thermal anomaly affecting the area. Boric acid is naturally contained in Larderello geothermal fluids, and it is quantitatively transferred into brine during steam condensation. This is the reason why it is still used to evaluate drift (droplets of condensable phase transported out of the cooling tower) through a simple mass balance. The available data on ancient fluid composition have been used to calculate: (a) the amount of geothermal fluid flowing in the areas, calculated by dividing the yearly production of boric acid by boric acid concentrations in the fluid, (b) the amount of Non-Condensable Gases (NCG), calculated according to the ancient geo-fluid gas content data and, finally, (c) the carbon dioxide emissions, calculated using gas compositional data. The available data include the annual boric acid (\(Q_{H_{3}BO_{3}}\)) production of the ancient Larderello area industries that have been running since 1818 ([PERSON], 1971; [PERSON], 1972; [PERSON], 1973), as well as an analysis of production data up to 1867 ([PERSON], 1972), but data on boric acid production after 1900 are not available due to the beginning of electric power production and deep drilling ([PERSON], 1972). By the value of measured ([PERSON] et al., 2021) boric acid concentration in steam, \([H_{3}BO_{3}]\), and the oldest available data of gas content in steam (\(G/V\)), the amount of gas and steam natural emission has been calculated. The production and boric acid concentration can be combined to calculate the amount of condensable fluid carrying boric acid with the following criteria:  
\[Q_{cond.}=\frac{Q_{H_{3}BO_{3}}}{[H_{3}BO_{3}]} \tag{4}\]  
where \(Q_{cond. }\), \(Q_{H_{3}BO_{3}}\) and \([H_{3}BO_{3}]\) are, respectively, the condensable flow rate, the boric acid production and the boric acid concentration in the condensable phase. The total amount of fluid (condensable phase + NCG), \(Q_{fluid}\), including the non-condensable gases' (NCG) flow rate, \(Q_{NCG}\), is then calculated.