Infrared window

[1] The window plays an important role in the atmospheric greenhouse effect by maintaining the balance between incoming solar radiation and outgoing IR to space.

In the Earth's atmosphere this window is roughly the region between 8 and 14 μm although it can be narrowed or closed at times and places of high humidity because of the strong absorption in the water vapor continuum or because of blocking by clouds.

In those days, computers were not available, and Simpson notes that he used approximations; he writes about the need for this in order to calculate outgoing IR radiation: "There is no hope of getting an exact solution; but by making suitable simplifying assumptions ...

The short wavelength boundary of the atmospheric IR window is set by absorption in the lowest frequency vibrational bands of water vapor.

Over the Atlas Mountains, interferometrically recorded spectra of outgoing longwave radiation[11] show emission that has arisen from the land surface at a temperature of about 320 K and passed through the atmospheric window, and non-window emission that has arisen mainly from the troposphere at temperatures about 260 K. Over Côte d'Ivoire, interferometrically recorded spectra of outgoing longwave radiation[11] show emission that has arisen from the cloud tops at a temperature of about 265 K and passed through the atmospheric window, and non-window emission that has arisen mainly from the troposphere at temperatures about 240 K. This means that, at the scarcely absorbed continuum of wavelengths (8 to 14 μm), the radiation emitted, by the Earth's surface into a dry atmosphere, and by the cloud tops, mostly passes unabsorbed through the atmosphere, and is emitted directly to space; there is also partial window transmission in far infrared spectral lines between about 16 and 28 μm.

As a proposed management strategy for global warming, passive daytime radiative cooling (PDRC) surfaces use the infrared window to send heat back into outer space with the aim of reversing rising temperature increases caused by climate change.

[13][14] In recent decades, the existence of the infrared atmospheric window has become threatened by the development of highly unreactive gases containing bonds between fluorine and carbon, sulfur or nitrogen.

The impact of these compounds was first discovered by Indian–American atmospheric scientist Veerabhadran Ramanathan in 1975,[15] one year after Roland and Molina's much-more-celebrated paper on the ability of chlorofluorocarbons to destroy stratospheric ozone.