Question

Radiation from the sun often gets trapped in the earth's atmosphere. What is the reason for this?

Answer 1

see below

Explanation:

electromagnetic radiation hitting the matter interact with it accordind with the chemical bonds of the molecules hitted . This bonds pass from a foundamental state to an excitated state, assorbing the radiations, and to do this passage need a fixed energy that is given only by a certain elecrtomagnetica radiation characterized by a specific wavelength.
So, for example `O_2` with a double bond adsorbs the radiation under 200 nm, so does also `N_2` that has a triple bond and under this wavelenght we have complete opacity.

The stratosferic `O_3` ,that has a triple risonant bond, adsorb between 200 and 300 nm (UV rays). Over tue 800-1000 nm we have an IR absorbation due to the stretching and to the bending of the bonds of Water, carbon dioxide and organic compounds as methane (greenhouse effect). On this principe are basad some type of chemical analysis thanks to wich we have known the chemical composition of sun and others stars

Answer 2

Greenhouse gases.

Explanation:

Greenhouse gases are gases that allow radiation of 0.5 micron wavelength to free pass through but block radiation around 10 microns.

http://www.oocities.org/marie.mitchell@rogers.com/GreenhouseEffect.html

The charts above show for various gases, what radiation wavelength is absorbed by that gas. The absorption is shown in green (except the bottom chart). The wavelength between the 2 red lines is the main wavelength for radiation from the sun. This is also known as visible light. You will see that there is almost zero absorption by any of the gases of this wavelength. Therefore the radiation passes through freely.

If you look at the absorption above 1 micron you will see quite a bit of absorption at various wavelengths. These wavelengths are called infrared but more importantly sensible heat. That is heat you can feel.

What makes this important is that when visible light hits the surface of the Earth, it is absorbed and there is an increase in energy of the Earth. This energy is released at longer wavelengths, generally speaking as heat.

So in summary, solar radiation is not absorbed by the atmosphere but when it is transformed into terrestrial radiation it is absorbed (or trapped if you prefer).