Near-surface atmospheric concentrations of greenhouse gases (CO2 and CH4) in Florence urban area: Inferring emitting sources through carbon isotopic analysis

From February to April 2019, near-surface CO2 and CH4 concentrations and carbon isotopic compositions (δ13C-CO2 and δ13C-CH4) were monitored at four stations belonging to the local air quality surveillance network of Florence (central Italy), representing typical zones of suburban background (SB), urban traffic (UT) and urban background (UB). The GHGs (greenhouse gases) concentrations showed a high spatial variability likely related to variable contributions from distinct emitting sources in the urban landscape. The δ13C-CO2 and δ13C-CH4 values suggested that domestic heating is the dominant GHGs emitting source at the UB station. Conversely, traffic-related CO2 emissions (about 74%) largely overwhelmed those from natural gas combustion at the UT stations, where vehicular exhaust emissions also affected atmospheric CH4 levels. The SB and UB stations registered the presence of multiple CH4 sources, which included both leakage from underground pipeline network for natural gas supply and biogenic emissions from urban waterways. These results offer a pivotal background framework to improve the performance of GHGs reduction policies and refine the spatiotemporal resolution of bottom-up estimations of urban GHG emissions.