Abstract. Ground-based thermal emission measurements of the zenith sky have been made at Peterborough, Ontario since January 1993. In this paper, the measurement of the Nu₆ band of atmospheric CFC-12, an important greenhouse gas, is presented for a cold, clear day in January 1994. A spectrum of the non-CFC-12 emission features has been simulated using the FASCD3P radiation code and measured radiosonde profiles of temperature, pressure and humidity. This has enabled a satisfactory subtraction of the interfering emission features from the CFC-12 emission spectrum. A comparison of the observed and simulated Nu₆-bands of CFC-12 shows good agreement at all frequencies of emission. From these spectra the total downward greenhouse radiative flux from the CFC-12 Nu₆ emission based for a very cold day has been estimated to be 0.27 W m^–2±10%.