Ground-based measurements of the thermal emission from the clear zenith sky have been made which clearly show the &ngr;4 band of CFC-11 (or CCl3F). An atmospheric water spectrum has been derived from these measurements and used to subtract the water emission features from the thermal emission spectra. These observations have been compared to line-by-line atmospheric radiance calculations using the FASCD3P algorithm. The agreement of the atmospheric CFC-11 emission band between the simulated result and the observed water-subtracted result is good. From these measurements the total downward greenhouse flux from the CFC-11 &ngr;4 emission band has been found to be 0.25 W/m2¿10%. ¿ American Geophysical Union 1994