# Why is such strange characteristic of the atmosphere?

**URL:** <https://boards.straightdope.com/t/why-is-such-strange-characteristic-of-the-atmosphere/945958>\
**Category:** Factual Questions\
**Created:** [July 8, 2021, 7:19am UTC](https://boards.straightdope.com/t/why-is-such-strange-characteristic-of-the-atmosphere/945958 "2021-07-08T07:19:31Z")\
**Posts on this page:** 1\
**Showing post:** 6

<div class="post-metadata">

**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\
**Post date:** [July 9, 2021, 7:47am UTC](https://boards.straightdope.com/t/why-is-such-strange-characteristic-of-the-atmosphere/945958/6 "2021-07-09T07:47:53Z")

</div>

> [@dtilque](#):
>
> > [@](#):
> >
> > Also, why don’t O2 & N2 absorb radiation? Does the fact that they have homogeneous atoms have something to do with absorbability?
> 
> As your cite say, O2 does absorb some in the gamma-UV part of the spectrum, although I believe that it’s mostly ozone (O3) that does the job there. I don’t know where the absorption lines for N2 are. It must absorb some wavelengths, but perhaps they’re in the same place as other absorption lines.

The issue is not that O₂ and N₂ do not absorb radiation, but that they do so in the far-infrared and ultraviolet wavelengths rather than the visible/near-IR band discussed here, and not very intensely. The exact absorption spectra depend on temperature and pressure as well as the exact mix of gases, etc., but you can get an idea by looking up parameters in a database, e.g., [HITRANonline line-by-line search: 1. Select Molecules](https://hitran.org/lbl/)

On the other hand, H₂O will totally absorb a lot of near-infrared wavelengths as you can see from your picture, while visible radiation is not very much absorbed by atmospheric gases.

See also  
[http://irina.eas.gatech.edu/EAS8803\_Fall2009/Lec6.pdf](http://irina.eas.gatech.edu/EAS8803_Fall2009/Lec6.pdf)  
and previous threads on the topic

> [@Infrared absorption by N2 vs CO2](https://boards.straightdope.com/t/infrared-absorption-by-n2-vs-co2/670977):
>
> In this weeks issue of Norway’s leading engineering journal a reader’s letter poses the following challenge/question: To me that looks like something I’d grade a high school student down for writing, since I found what looks to me like coherent explanations and empirical data just by opening the Wikipedia articles on Nitrogen, CO[sub]2[/sub] and greenhouse gases. But just so I don’t get caught by some nitpick gotcha after I berate the journal for giving an obvious moron a platform I thought I’…

---

_[View the full topic](https://boards.straightdope.com/t/why-is-such-strange-characteristic-of-the-atmosphere/945958)._