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- Title
Seasonal and diurnal variations of greenhouse gases in Florence (Italy): inferring sources and sinks from carbon isotopic ratios.
- Authors
Venturi, Stefania; Tassi, Franco; Cabassi, Jacopo; Gioli, Beniamino; Baronti, Silvia; Vaselli, Orlando; Caponi, Chiara; Vagnoli, Carolina; Picchi, Giorgio; Zaldei, Alessandro; Magi, Francesco; Capecchiacci, Francesco
- Abstract
By 2050, more than two-thirds of global population is expected to live in urban areas. Inorder to guarantee a sustainable development and the achievement of the greenhouse gas(GHG) emissions reduction set by the Paris Agreement, city administrators must adopt urbanplanning strategies and local policy initiatives aimed to lowering the urban carbonfootprint. The Municipality of Florence (Italy) has recently renewed its intent tocut urban CO2 emissions of 50 % by 2030 through a series of actions aimed todecrease GHGs contributions from vehicular traffic by amending citizens attitudestowards urban mobility. Nevertheless, Florence is still affected by poor air qualityconditions.The effectiveness of intervention plans depends on the availability of a clear and completeknowledge of the emitting sources and their relative contributions to urban air quality and hasto be verified with monitoring surveys of GHGs emissions and concentrations. This studypresents the results of a continuous monitoring (from 7 to 21 July, 2017 and from October 10to December 15, 2017) of (i) CO2 fluxes, and (ii) atmospheric CO2 and CH4 concentrationsand carbon isotopic ratios (δ13C-CO2 and δ13C-CH4) from a monitoring site located in thecity centre.CO2 flux data revealed that the metropolitan area acted as a net source of CO2 during thewhole observation period. The separation of the different anthropogenic contributions toatmospheric CO2, investigated on the basis of the Keeling plot analysis, revealedgasoline combustion contributing for about 30 % and natural gas combustion forabout 70 %, with the latter contributing 7 times more in December than in July. Themeasured CO2 fluxes were about 80 % larger in autumn than in summer, furtherconfirming that domestic heating based on natural gas is the dominant CO2 emittingsource in Florence. The current urban green infrastructures are not sufficient tocounterbalance the emissions from anthropogenic sources, even during the plantsvegetative season. Nevertheless, the continuous monitoring revealed a δ13C-CO2shift in October, during the central hours of the day, towards values lower thanthose expected for simple mixing between background and anthropogenic CO2,suggesting that photosynthetic withdrawal of atmospheric CO2 might partiallycontribute to reduce CO2 concentrations at peculiar periods prior to the heatingseason.During autumn, atmospheric CH4 concentrations sensibly increased with respect to summerlevels, whilst δ13C-CH4 shifted towards heavier values. The diurnal isotopic ratios of CH4 inJuly were relatively constant, pointing to the absence of relevant local emitting sources duringdaytime, and oscillated around -51 ‰ vs. V-PDB, i.e. a value typical of biogenic sources.During fall, monthly average δ13C-CH4 values around -45 ‰ vs. V-PDB confirmed theoverwhelming contribution from natural gas, likely related to CH4 leaks from thecity distribution network. However, in October, a peak towards heavier δ13C-CH4values was observed in working days during the afternoon rush hour (around 17:00),suggesting that also vehicular exhaust emissions partially contribute to atmospheric CH4.
- Subjects
FLORENCE (Italy); CARBON isotopes; SEASONAL temperature variations; NATURAL gas; GREENHOUSE gases; COMBUSTION gases; METROPOLITAN areas; GREENHOUSE gas laws; CARBON cycle
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article