This dataset provides in situ airborne measurements of atmospheric carbon dioxide (CO2) over Indianapolis, Indiana (IN) on September 3, 2014 during the morning commuter period with heavy traffic emissions. Stationary source emissions are also included. The observed CO2 plume downwind of the urban area, along with the prevailing wind speed and direction, enabled estimations of emission rates. CO2 was measured with an airborne CO2 Laser Absorption Spectrometer (JPL CO2LAS) developed at NASA's Jet Propulsion Laboratory (JPL) to demonstrate the airborne Integrated Path Differential-Absorption (IPDA) lidar technique as a stepping stone to a capability for global measurements of CO2 concentrations from space. The CO2LAS measures the weighted, column averaged carbon dioxide between the aircraft and the ground using a continuous-wave heterodyne technique. The instrument operates at a 2.05 micron wavelength optimized for enhancing sensitivity to boundary layer carbon dioxide. Measurements were taken onboard a DC-8 aircraft during this Active Sensing of CO2 Emissions over Nights, Days and Seasons (ASCENDS) airborne deployment. The data are provided in HDF-5 format.