I know the mechanism of how ozone absorbs UV but why is it that no other molecules do this?

Is there any special reason?

PS: If I'm mistaken and there are other molecules that can absorb UV please mention them.

  • 2
    $\begingroup$ Do you just mean in the atmosphere or in general? In general, there are lots molecules which absorb UV light. One everyday example is sunscreen, which, depending on the formulation, contain compounds that absorb UVA and UVB light. compoundchem.com/2014/06/05/sunscreenchemicals $\endgroup$
    – Tyberius
    Mar 4 '17 at 5:31
  • $\begingroup$ In atmosphere. And also ur comment gave me another question. If ozone absorbs UV radiation...Why do we need UV protection using sunscreen? Is it that not all UV gets absorbed? $\endgroup$ Mar 4 '17 at 5:33
  • 1
    $\begingroup$ I think a good answer to this is under another question here:chemistry.stackexchange.com/questions/35734/… The first answer gives an explanation of how both ozone and oxygen absorb UV. In regards to your second question, there isn't enough ozone (or other UV absorbing compounds) to perfectly screen the Earth's surface. In addition, ozone absorbs only specific wavelengths of UV light, so other UV wavelengths could get through. $\endgroup$
    – Tyberius
    Mar 4 '17 at 5:41
  • $\begingroup$ Although you ask about ozone and UV light, the process is completely general is the same for any molecule, chlorophyll in plants, the dye in your T shirt, ink on paper etc. In the molecule, if the photon has the right amount of energy, it excites an electron to a higher molecular orbital and so forms an excited state. The photon is absorbed and so destroyed in the process. We see this as a colour (in transmitted or reflected light) if it occurs in the visible region of the spectrum. If it occurs in the UV we can't detect it by eye but can with photodetectors. $\endgroup$
    – porphyrin
    Mar 4 '17 at 18:28
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    $\begingroup$ You should edit your question to ask that then. $\endgroup$ Mar 12 '17 at 17:43

The ISO 21348 Definitions of Solar Irradiance Spectral Categories defines UV radiation as that portion of the electromagnetic spectrum having wavelengths from 10 to 400 nm. Different atmospheric compounds absorb more or less strongly than others throughout the UV portion of the spectrum.

The following table was reproduced from this Wikipedia article:

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Although not fully quantitative, this table indicates that nitrogen, oxygen and ozone all absorb different portions of the UV spectrum. Water vapor is also an important UV absorber that is not discussed in the above table.

Also, regarding the UV absorption of (liquid) water and your comment that "It is widely accepted that life on Earth wouldn't be possible without ozone layer", it was in large part the protection from UV radiation afforded by liquid water that allowed aquatic organisms to survive prior to the existence of the ozone layer. If the ozone layer were to vanish today, although the nature of Earth's biosphere would change drastically, I suspect many aquatic species, particularly microbes, would adapt and continue to survive in the absence of an ozone layer. It would be bad news for you and me though ;)


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