# Atmosphere on the Moon

Question: How would you make a breathable atmosphere in an artificial closure on the Moon?

I originally thought that simply obtaining water from the Moon, sending an electrical current through it to get Hydrogen and Oxygen was sufficient enough to have humans breathe on the Moon.

But upon further research, I learned that too much oxygen is actually toxic to your body, and it will kill you. Meaning you need the right balance of other gases in the atmosphere to make it breathable.

So my question is simple: What are the required gases needed in the atmosphere, such that humans can breathe and do normal activities? The atmosphere is composed of $78\%$ Nitrogen, $21\%$ Oxygen, $1\%$ Argon and then the rest is traces of other gas. Such as Helium, Carbon Dioxide, Carbon Monoxide, Methane, Krypton, etc.

Which of these gasses should you keep, and which should you drop when creating a breathable atmosphere on the Moon? I think you'll have to keep Nitrogen, Oxygen and Argon, but I'm not sure how you can obtain Nitrogen and Argon.

• We can live in a 100% oxygen atmosphere. This was used in Appolo 1 for instance. This is however a bad idea for other reasons (fire safety). They keyword here is "partial pressure" Argon is not needed for life support. See en.wikipedia.org/wiki/Breathing_gas for other gas used for breathing. – Antzi Oct 25 '16 at 4:48
• Do you mean an atmosphere within an artificial enclosure on the Moon, or do you mean producing a breathable atmosphere everywhere on the Moon? If it's everywhere outdoors, the Moon's regolith may become a frustrating sink - constantly reacting with and absorbing some of the oxygen, and with the constant UV from the sun, a low pressure oxygen atmosphere may have a non-zero amount of ozone (O${}_3$) near the surface with is nasty for people - according to Wikipedia 100 parts per billion can be harmful with long term exposure. – uhoh Oct 25 '16 at 12:28
• @uhoh I meant an atmosphere with artificial enclosure. – Frank Oct 25 '16 at 12:39

The only gases relevant to life will be oxygen, nitrogen, carbon dioxide, water vapor, and methane (not counting all the volatile compounds of CHNOPS present in trace amounts). Of those, the only one necessary for human life support is oxygen; the rest are either helpful/necessary for plant life or a by-product of life you would likely need to manage or remove.

For human habitation, you will need 3psi partial pressure of oxygen to make available the same amount as in sea level air. But a 3psi atmosphere might not be very human-friendly - if warm enough for comfort at rest, you could overheat in it when active. Add some nitrogen; could probably get away with much less than sea-level equivalent. Some humidity would be a good thing too.

As stated before, there is no need for anything besides oxygen to sustain human life.

Pure oxygen has been used (and still is used) when there is need for a low pressure inside a spacecraft. As moon has a much lower gravity this might be same when we would consider a hypothetial atmosphere. Unfortunatelly its gravity is so low it can not hold any substancial atmosphere...

It still does have a little of an atmosphere, but is is so thin one can not really call it anything.

When considering the inside of a moon-station there are different methods how to create an atmosphere inside - from 100% oxygen on low pressures ( = thin hulls ) to a "normal" atmosphere (though anything beside oxygen and nitrogen (and a little humidity) is not used by humans...) on normal pressures.

Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

• Then why do some websites saying that breathing in pure oxygen will overload your blood stream and kill you? – Frank Oct 25 '16 at 12:39
• @Frank "100% oxygen on (at) low pressures" is the clue. An atmosphere of pure oxygen at 21% of normal atmospheric pressure will give you roughly the same oxygen into your blood as 21% oxygen (the rest non-soluble/inert) at normal pressure. It's roughly the same number of oxygen molecules colliding with the inside of your lungs per second either way. However, on earth, unless you are in a plane at high altitude or in an experiment, you'll probably be near normal atmospheric pressure and therefore in that case pure oxygen could be bad. – uhoh Oct 25 '16 at 13:13
• @Hans You're answer seems reasonable, but could benefit from a few links to sources. You are essentially describing how 'partial pressure' works without ever naming it or citing a source. en.wikipedia.org/wiki/Partial_pressure – OrangePeel52 Oct 25 '16 at 13:48