Methane and carbon dioxide fluxes and source partitioning in urban areas: the case study of Florence, Italy.

Long-term fluxes of CO(2), and combined short-term fluxes of CH(4) and CO(2) were measured with the eddy covariance technique in the city centre of Florence. CO(2) long-term weekly fluxes exhibit a high seasonality, ranging from 39 to 172% of the mean annual value in summer and winter respectively, while CH(4) fluxes are relevant and don't exhibit temporal variability. Contribution of road traffic and domestic heating has been estimated through multi-regression models combined with inventorial traffic and CH(4) consumption data, revealing that heating accounts for more than 80% of observed CO(2) fluxes. Those two components are instead responsible for only 14% of observed CH(4) fluxes, while the major residual part is likely dominated by gas network leakages. CH(4) fluxes expressed as CO(2) equivalent represent about 8% of CO(2) emissions, ranging from 16% in summer to 4% in winter, and cannot therefore be neglected when assessing greenhouse impact of cities.