In: Chemistry
Why is the region of the electromagnetic spectrum between 8 and 13 um known as the "atmospheric window"? Why are gases that absorb thermal IR in this range of particular concern? What are some of those gases?
(Note – local conditions like humidity also impact this window)
*Major Greenhouse gases like water vapour do not absorb in this wavelength range which makes it possible for heat to escape the earth
*Without this atmospheric window, Earth would become too warm to support life.
2. Gases that absorb thermal IR in this range are a concern because they prevent heat to escape from the earth. This disturbs the heat balance and gradual warming of earth will occur. Eventually Earth temperature will rise above habitable zone.
3. Examples of such gases
*Unreactive gases containing bonds between fluorine and either carbon or sulfur eg SF6 Sulphur Hexafluoride
Eg perfluorocarbons (CF4, C2F6, C3F8)
Note – Apart from F other halogens also absorb in the atmospheric window, though to lesser extent
*
*Also being unreactive , these gases persist in the atmosphere . They have high global warming potential- much more than Carbon Dioxide