[david.helmly]

Hey guys,

How easily do hydrogen and oxygen react with each other?  For example if I release a sample of hydrogen gas at sea level, I bet it will quickly start going up, but what will happen along the way?  Will it all rise to the top, or will much of it react with oxygen before it gets above the atmosphere's heavier gasses?

I've been working on a bigger-picture problem for some time now, what are the permanent effects of industry and natural phenomenae on the atmosphere's composition?  ...because if stuff (electrolysis, methane break-down, decomposing organic material, etc) is releasing hydrogen into the air and it does what it does: goes up! will it get out of the reach of being pulled back into normal hydrogen cycles and essentially add elevated oxygen levels to our atmosphere?

...but to answer that I just need a ballpark idea of what happens to hydgrogen released at the bottom of our atmosphere: does it reach the top?  or will it react with oxygen on the way?

Who knows the chemistry of the mid to upper atmosphere?

[billnotgatez]

http://en.wikipedia.org/wiki/Brownian_motion

Is this also an alternative?

[david.helmly]

Cool!  That's foundational to this problem.

With it we can calculate how long it will take this sample of hydrogen molecules to reach the upper atmosphere.

But before the sample gets there, how reactive is it to all the oxygen it will pass?  Will the even more reactive ozone molecules increase hydrogen reaction?  Will the thermosphere, with high energy, low density, air molecules change anything?

[nj_bartel]

I believe it would take something like a lightning bolt to get oxygen to react with hydrogen in the atmosphere.

[billnotgatez]

This is just an interesting link on the atmosphere.

http://www.engr.colostate.edu/~ramirez/ce_old/classes/ce422_ramirez/CE422_Web/WaterVapor/water_vapor_CE322.htm

@david.helmly
Now for my question.
if hydrogen stratifies to the top of the atmosphere, why do we have ~80 nitrogen on the earth's surface.

@nj_bartel
although it is conventional to expect a spark to ignite hydrogen, is there other energy sources that could do the same. I think UV can combine hydrogen and Chlorine.

[DrCMS]

It is my understanding that hydrogen gas has enough kinetic energy to reach escape velocity and leave our atmosphere completely.

http://en.wikipedia.org/wiki/Atmospheric_escape

[nj_bartel]

A certain percentage have enough energy to reach escape velocity is my understanding as well.

[david.helmly]

@billnotgatez
Thanks for the link...good stuff!

if hydrogen stratifies to the top of the atmosphere, why do we have ~80 nitrogen on the earth's surface?

Because the nitrogen has to contend with the oxygen, which is because the two molecules are almost the same mass.  For example:
Nitrogen molecule (N2): 28 amu - spread through most altitudes
Oxygen molecule (O2): 32 amu - spread through most altitudes until UV takes it out above the ozone layer
Hydrogen molecule (H2): 2 amu - most is in the upper atmosphere
methane molecule (CH4): 16 amu - has some spread...definitely more dense (/volume) as you go higher

[david.helmly]

although it is conventional to expect a spark to ignite hydrogen, is there other energy sources that could do the same. I think UV can combine hydrogen and Chlorine.

Exactly, and UV is my number one concern.  I'll look into Chlorine too, thanks!  What I still can't find even for UV is how much does it affect oxygen + hydrogen reaction?

[david.helmly]

@DrCMS & nj_bartel
Yes, that is exactly what's going on here, driving the process of hydrogen removal (and therefore implicite oxygen addition) to the atmosphere.

How fast is it driving the process?   How much hydrogen is up there and how does that affect escape rates?  How fast does hydrogen get up there?  What's the survival rate of hydrogen released at the bottom of the atmosphere?  Where (if anywhere) does it get "hung up" or taken out by reactions etc?

That's the level of explicit detail that is running laps over my head.

[nj_bartel]

You're looking at some pretty nightmarish computations in my opinion 

[david.helmly]

excellent!  Where there's a challenge there's knowledge to be gained =)

[Shoofly]

The answer that significant amounts of hydrogen gas just exits the atmosphere due to its terminal velocity is kind of hard to fathom.  Wouldn't most of the hydrogen react either on the way up or in the ozone layer.  Is there more to this "exit the atmosphere" answer?