The demonstration of thermal infrared quantum cascade laser heterodyne spectrometry to resolve local thermodynamic equilibrium molecular emission lines from earth's atmospheric constituents is presented. The instrument is described, as well as the early steps towards radiometric calibration. Room temperature ethylene emission line measurements carried out in the laboratory are used to validate the instrument. High-resolution (0.02 cm-1) emission lines from atmospheric carbon dioxide and water vapor are then recorded in a zenith-looking configuration and compared to a radiative transfer model and ideal instrument model expectations.