The Composition of Earth’s Atmosphere With Elevation

In researching a post about the Kármán Line I discovered the NASA MSIE E-90 atmosphere model (thanks to Rhett Allain) which models the composition of Earth’s atmosphere up to an elevation of 1000?km. I found it very interesting.

atmosphere-composition-all

Up to around 100?km the composition is fairly “normal”, in that it’s what we surface-dwellers would expect: mostly molecular nitrogen (N2 rather than N) and molecular oxygen (O2) with a small amount (0.93%) of argon and traces of some other gases (carbon dioxide, neon, etc.).

After 100?km the percentage of molecular nitrogen and molecular oxygen decrease sharply, and there is a similarly sharp increase in monatomic and triatomic oxygen, better known as ozone (i.e. this represents the “ozone layer”). There is also a small increase in the percentage of monatomic nitrogen and nitrogen compounds, and argon disappears entirely.

By 200?km ozone dominates, and this continues to about 650?km where helium takes over as the predominant component. Monatomic nitrogen and nitrogen compound concentration peaks at around 500?km, with an overall concentration of 1.6%.

By the time we reach an elevation of 1000?km helium makes up 93% of the atmosphere. This is due to the fact that helium is an unreactive and very light atom (with a mass about one-eighth of oxygen) and thus isn’t held tightly by Earth’s gravitational field. (Helium is so light that it can escape Earth’s gravity entirely.) The bulk of the remainder is hydrogen, also prevalent due to its low mass (about one-sixteenth of oxygen’s).

common-gases

The concentration of “normal” gases in the atmosphere with elevation.

uncommon-gases

The concentration of less common gases in the atmosphere with elevation.

It’s important to note that the graphs above all show concentration as a percentage of the total number of particles of gas in the atmosphere, rather than by mass or volume. The atmosphere becomes incredibly thin at high elevations, so that particles of gas may travel many kilometres between collisions, and if absolute concentrations were used instead, the graph would look very different (and be completely unusable, which is why I haven’t included it here).

7 thoughts on “The Composition of Earth’s Atmosphere With Elevation

  1. I thought I’d give the NASA MSIE E-90 atmosphere model a try. I’m getting different results from yours. For instance, I’m getting an O and H peak at 100 km, which is almost what I would expect. I would expect H to peak at 120 km. The temperature data from the model also seems high. I was expecting 0 C and the model gave me 127 C at 120 km. I don’t see an option for charting O3.

    Here’s the app I’m using. Perhaps you’re using a different one.
    http://ccmc.gsfc.nasa.gov/modelweb/models/msis_vitmo.php

    As I understand it, the upper heterosphere, at a distance greater than 100 km (the limit of Earth’s atmosphere, the Kármán line) and up to 120 km altitude, is composed almost exclusively of hydrogen. The temperature at 100 km is -86 C and the temperature at 120 km is 0 C. There are seasonal variation in molecular oxygen near 100 km altitude. The density of hydrogen (H2), is 0.55 ppmv within the heterosphere.

    I’m rather new to this info. Can you tell if I’ve obtained old and out-dated data?

    But, aside from all that, I actually stopped by with a question. I think you’ve answered it partially already – “particles of gas may travel many kilometres between collisions”. Given my current understanding of the homosphere and heterosphere, I’m wondering why there hasn’t been a notable reaction between the oxygen and hydrogen. Aren’t particle proximity and a spark all that are needed for an explosion?

    You’re comment would be appreciated. Thanks for posting your graphs and naming your data source. Please do let me know if you have a different app link.

    Thanks again. :-)

  2. Theresa,

    The date and (more so) the longitude/latitude will make a big difference to the results you achieve. I suspect that is the source of our differing results. I used the same source as you.

    With regards to a reaction between hydrogen and oxygen, you need a certain concentration for those sides of the fire triangle (i.e. fuel and oxygen) to be complete.

  3. Thank you for the answers, Mr. Reid. The numbers I’m getting are based on the app’s default coordinates.: lat=55, long=45. I’m using Jun 21 2014 for the date this time, but the defaults were used previously and there’s no noticeable difference. I’m outputting to plot. It seems that the plot doesn’t accurately represent the data in the list output. For example, in the plot, there are no reported N2, O2, H2, or Ar above 50 km.

    At the Kármán line, O = 2,336,000 molecules / km3 and H = 121.3 molecules / km3, according to the data I see in the list output. At 3 kg of hydrogen per second escaping the troposphere, I suppose it’s just a matter of time for concentrations to accumulate.

    Thank you for responding.

  4. Here’s a thought – maybe the Tunguska Explosion of 1908 was a result of an Oxygen-Hydrogen collision. Monatomic oxygen is present from 80 km and up.

  5. No, definitely not. There is really no evidence that the Tunguska Event was anything other than a meteor strike (though it wasn’t actually a “strike”, the meteor exploded in mid-air).

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