A measurement of the greenhouse radiation associated with carbon tetrachloride (CCl4)

Ground-based, thermal emission measurements of the cold, clear sky have been made showing the ν3 fundamental emission band of carbon tetrachloride (CCl4) which is located in the 786–806 cm−1 region. A spectrum of the non-CCl4 background emission features has been simulated using the FASCD3P line-by-line radiation code with measured radiosonde parameters of pressure, temperature and humidity. The simulated spectrum has been used to extract the CCl4 thermal emission band from the atmospheric emission spectrum. A tropospheric CCl4 mixing ratio of 170±30 pptv was determined from these measurements. In addition, the downward long-wave flux associated with the ν3 emission band of CCl4 measured at the surface has been estimated to be 0.09 W/m² with an uncertainty of 15–20%. This flux is about one third and one fifth of that corresponding to the chlorofluorocarbons CFC-11 and CFC-12, respectively.