Map of ground-based tower locations (numbers and black stars mark different towers) in Indianapolis (39.363 N–40.137 N, 86.667 W–85.654 W) and daytime (13–19 local standard time) average surface CO₂ fluxes (shade) during the first 10 days of September 2013. All towers have CO₂ mole fraction measurements, and towers 1, 2, 3, 5 and 9 have ¹⁴C content and CO mole fraction measurements. Surface CO₂ fluxes consist of fossil fuel CO₂ emissions (Hestia inventory data) and biogenic CO₂ fluxes simulated from the Vegetation Photosynthesis and Respiration Model (VPRM). Since the CO₂ff emissions at some strong point sources (such as the Harding Street Power Plant and some industrial emission points) have emissions per unit area that are more than 10 times larger than most of the city area but cover only 3 percent of all the grid points, we limited the maximum range of emissions to 15 μmol m^–2 s^–1 to show the spatial distribution of daytime average CO₂ fluxes. DOI: https://doi.org/10.1525/elementa.138.f1