The effective solar radiation intensity, as observed through the atmospheric window between 16 mu and 24 mu, is determined by comparison with the observed radiation intensity of the earth's surface (thermocouple) below 13 mu. The ratio of the effective value to the value calculated for T = 6000°K is the transparency of the atmosphere to solar radiation within the interval 16 mu–24 mu. Opacity in this spectral region is due largely to water vapor and carbon dioxide. Provisional estimates of percent transmission, probably lower limits, are found to be:
The net loss of energy by the earth’s surface, through the 16-mu-24-mu window, is small, but probably not negligible from a meteorological point of view.
ARTHUR ADEL, "An Estimate of Transparency of the Atmospheric Window 16 Mu to 24 Mu," J. Opt. Soc. Am. 37, 769-769 (1947)