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. Threats 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, one year after Roland and Molina's much-more-celebrated paper on the ability of chlorofluorocarbons to destroy stratospheric ozone. The "stretching frequencies" of bonds between fluorine and other light nonmetals are such that strong absorption in the atmospheric window will always be characteristic of compounds containing such bonds, although fluorides of nonmetals other than carbon, nitrogen or sulfur are short-lived due to hydrolysis. This absorption is strengthened because these bonds are highly polar due to the extreme electronegativity of the fluorine atom. Bonds to other halogens also absorb in the atmospheric window, though much less strongly. Moreover, the unreactive nature of such compounds that makes them so valuable for many industrial purposes means that they are not removable in the natural circulation of the Earth's lower atmosphere. Extremely small natural sources created by means of radioactive oxidation of fluorite and subsequent reaction with sulfate or carbonate minerals produce via degassing atmospheric concentrations of about 40 ppt for all perfluorocarbons and 0.01 ppt for sulfur hexafluoride, but the only natural ceiling is via photolysis in the mesosphere and upper stratosphere. It is estimated that perfluorocarbons (, , ), originating from commercial production of anesthetics, refrigerants, and polymers can stay in the atmosphere for between two thousand six hundred and fifty thousand years. This means that such compounds have an enormous global warming potential. One kilogram of sulfur hexafluoride will, for example, cause as much warming as 23 tonnes of carbon dioxide over 100 years. Perfluorocarbons are similar in this respect, and even carbon tetrachloride () has a global warming potential of 1800 compared to carbon dioxide. These compounds still remain highly problematic with an ongoing effort to find substitutes for them. See also Greenhouse effect Greenhouse gas Infrared astronomy Optical window Ozone depletion Radio window References Books External links IR Atmospheric Window Atmospheric radiation Satellite meteorology Electromagnetic spectrum Climatology Climate change Atmosphere