Which electromagnetic radiations do Greenhouse gases absorb? Is it only Infrared or a range of wavelengths? Please specify the range of wavelength of radiations. More Specifically, the question...

Which electromagnetic radiations do Greenhouse gases absorb? Is it only Infrared or a range of wavelengths? Please specify the range of wavelength of radiations.

More Specifically, the question is: Methane is a Greenhouse Gas because it absorbs longer wavelengths of the electromagnetic spectrum while transmitting shorter wavelengths?

Infrared radiations are of order 10^-4 so they should be considered shorter. Right?

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ncchemist | eNotes Employee

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When dealing with radiation in the atmosphere, you are basically dealing with three different type of radiation, ultraviolet (UV), visible, and infrared (IR).  UV light ranges from 100 nm to 400 nm, visible light ranges from 400 nm to 700 nm, and IR light ranges from 700 nm to 1,000 nm.  So in terms of wavelength, the order from shortest to longest is UV<visible<IR.  But energy is inversely proportional to wavelength, so UV is the highest in energy and IR is the lowest in energy.

Greenhouse gasses are gasses in the atmosphere that absorb and trap in heat near the surface of the Earth.  We know that visible light passes though greenhouse gasses because we can see it here on the Earth's surface.  We also know that UV radiation makes it through the atmosphere since we have to wear sunscreen to protect ourselves from it.  So greenhouse gasses allow shorter wavelengths to pass through but absorb longer wavelengths (IR).  So that makes the correct answer: Methane is a Greenhouse Gas because it absorbs longer wavelengths (e.g., IR) of the electromagnetic spectrum while transmitting shorter wavelengths (e.g., UV).

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