Infrared absorption cross sections for acetone (propanone), CH 3 C(O)CH 3 , have been determined in the 3μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125HR) and a multipass cell with a maximum optical path length of 19.3m. The spectra of mixtures of acetone with dry synthetic air were recorded at 0.015cm −1 resolution (calculated as 0.9/MOPD using the Bruker definition of resolution) at a number of temperatures and pressures (50–760Torr and 195–296K) appropriate for atmospheric conditions. Intensities were calibrated using three acetone spectra (recorded at 278, 293 and 323K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.