Stable isotope composition and airborne concentration of CO2 in Rome capital city (Italy)

Airborne CO₂ has played a pivotal role in maintaining the Earth's atmospheric temperature at reasonable levels throughout its history. Since the onset of the industrial revolution, the level of airborne CO₂ has surged due to the combustion of hydrocarbons, leading to global warming. Hydrocarbon consumption is predominantly concentrated in metropolitan areas, driven by various human activities. Estimations of CO₂ emissions into the atmosphere rely on the growth of electrical power generation through hydrocarbon combustion. This study presents the outcomes of direct measurements of stable isotope concentrations in airborne CO₂ in the urban area of Rome, Italy. We focused on Rome capital city, because i) it is the most populous municipality in Italy (2.8 millions inhabitants), ii) it is the European municipality with the largest surface of green areas and iii) in its south-east sector it borders the Colli Albani quiescent volcano. The dataset encompasses stable isotope compositions and airborne CO₂ concentrations gathered to investigate variations in CO₂ emissions across space and time. The spatial survey conducted throughout Rome's urbanized area, on a 250 km long path, aims to pinpoint the relevant sources of CO₂ based on the stable isotope signature. Results reveal that the combustion of fossil fuels, stemming from urban mobility and household heating, constitutes the predominant source for the excess of airborne CO₂ across a wide area of Rome centre. On the contrary, within the Rome south-east sector, including Colli Albani periphery, the carbon isotopic signature of airborne CO₂ discloses the endogenous origin of the gas emissions. Continuous monitoring was carried out by the installation of an isotope analyser in three specific points of interest throughout Rome: the busiest area of the city centre, the woodland urban park of Villa Ada and the endogenous gas emission of Cava dei Selci. Findings unveil cyclic variations in human-related CO₂ emissions in the city centre. The highest concentrations of airborne CO₂ coincide with rush hours during morning and evening. The urban park is not affected by anthropic CO₂ and its trend displays the typical day-night cycle. At Cava dei Selci we found high CO₂ concentrations by a volcanic source and variations in the urban area correlate with changes in environmental conditions, such as wind speed and direction.