The quantification of fossil-fuel derived carbon dioxide (CO2ff) emissions is critical for regional carbon budgets. Radiocarbon (14C) is an effective tool to estimate the contribution of CO2ff to the total atmospheric CO2. In the present study, we have determined the spatial distribution of fossil fuel derived CO2 across Delhi using 14C measurements in Peepal tree leaves from April 2016 to March 2017 at city scale. Our analysis results show that the Δ14C values vary between –67.78‰ to 5.61‰ and corresponding CO2ff values are varying from 1.63 ppm to 33.34 ppm. CO2ff values from campus sites vary between 6.99 ppm to 16.38 ppm with an average value of 10.22 ± 3.20 ppm, while CO2ff values vary from 2.41 ppm to 33.34 ppm with an average value of 13.32 ± 9.40 ppm for sites located in the parks. Further, we observed the higher contributions of fossil fuels in the CO2 from northwest Delhi, central Delhi, and some parts of east and southwest Delhi. In the absence of real-time CO2 monitoring, the results of this study provide a potential method for analyzing the contribution of CO2ff values over the urban landscape to total CO2 over the study region.