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From Wikipedia:
By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases.
For example, would humans be able to survive in these atmospheres? :
There are three separate issues here:
So a 100% oxygen atmosphere will not work, due to point 1. Also your 90% CO2 atmosphere won't work because the high CO2 concentration will kill you.
Whether the other 10% atmospheres will work depends on the total pressure. If the total pressure is twice as high as on earth, the partial pressure is the same as on earth, and since the other gases are inert (either nitrogen like here on earth, or noble gases), they should not make too much trouble on their own. However, with the exception of helium, they have narcotic effects, therefore the nitrogen, argon and xenon atmospheres would also not be the best to live in, although temporary visits should be less of a problem (thanks to Rob Watts for making me aware of this problem). Moreover, there should also be some CO2 for respiration to work.
With the 2% atmosphere, you'll need 10 times as much pressure to get the same partial pressure for oxygen as on earth. I'm not sure whether the human body could tolerate that for an extended time (for a limited time it certainly can, as divers prove; it's the pressure you find on earth under water in a depth of 90 meters). At those concentrations, you really should have helium as inert gas, however.
Another point: In all of the above I've assumed that the percentage is the one on the ground (because that's also where the earth atmosphere values are valid). On earth the oxygen fraction goes down with height because nitrogen is slightly lighter than oxygen. Of the other gases you mention, only helium is lighter than oxygen; however that one is much lighter, so in the helium-oxygen atmosphere, the oxygen percentage will quickly go down as you go up (note, however, that the partial pressure will go down no quicker than in our atmosphere, assuming the same gravitation). So in the helium-oxygen atmosphere, already a small mountain will hinder you from making fire (but not yet from breathing).
For the gases which are heavier than oxygen, the fraction of oxygen will grow as you go up. However, the partial pressure will still go down. Which gives the seemingly paradox situation that things burn better at greater height, while your body gets less oxygen.
100% oxygen is dangerous - stuff will burn, oxygenation can damage tissues. Apollo 1 had pure oxygen atmosphere, did not ended up well. oxygen is toxic
90% CO2 will kill you (not enough partial pressure of oxygen in hemoglobin)
2% of oxygen is not enough.
10% of oxygen with other inert gasses (nitrogen (not inert, but not reactive either), helium) might be survivable. See trimix breathing gas for scuba diving. Different mixes for different usage, and pro/com for helium and nitrogen, and lowering partial pressure of oxygen.
Seems than xenon is used for anesthesia, so it will do you no good to have it in such concentration. Thanks @Twelfth
Argon enhances change of gas embolism, but it was used to replace nitrogen to speed up decompression, so it seems NOT be immediately poisonous.
Apparently, well trained and adapted humans (with more hemoglobine in blood) can survive 12% of oxygen
Image at this page about limits of human survival shows dangerouns levels of hypoxia (low oxygen) and hyperoxia (too much oxygen).
Twelfth in his answer raised interesting aspect: relative density of different gasses, and possibility of separate layers. Looking at gas density table, air density (1.2 kg/m3) is close to oxygen (1.3) and nitrogen (1.16) - no surprise there.
Helium density (0.16) is 10% of oxygen, so likely atmosphere with mix of oxygen and helium would after a short time formed layers, with more oxygen at the lower layers - leading to oxygen poisoning. Not good. Even worse: @Marky Mark is right helium does escape from Earth atmosphere.
Argon is bit heavier then oxygen (1.66), but not much. But if such layer of argon was possible and stable, all lowlands would be uninhabitable. So you would need to add some winds and turbulence to mix stuff up. Even then, mines and cellars would not be possible without active ventilation, because heavier argon would accumulate there, causing asphyxiation.
At normal atmospherical pressure (101.325 kPa) if your only gas is O2 you will have a partial pressure of 101.325 kPa of O2... lethal, deadly and painful.
Lets talk about consequences!
$$ \left| \begin{array}{cc|ccc|c} \text{Gas}&\text{%}&\text{gr/mol}&\text{Mols}&\text{Fractal Mol}&\text{Partial Pressure (kPa)}\\ \text{O}_{2}&\text{10%}&31.9988&0.31&\text{8%}&8.98\\ \text{N}_{2}&\text{90%}&28.0134&3.21&\text{91%}&92.37\\ \text{Total}&\text{100%}&60.0122&3.52&\text{100%}&101.325 \end{array} \right| $$
In Wikipedia you can find another gr/mol values. This is because O2 and N2 are <2> atoms per molecule, so I multiply the value per atom by 2.
Values:
Concequences:
$$ \left| \begin{array}{cc|ccc|c} \text{Gas}&\text{%}&\text{gr/mol}&\text{Mols}&\text{Fractal Mol}&\text{Partial Pressure (kPa)}\\ \text{O}_{2}&\text{10%}&31.9988&0.31&\text{12%}&12.34\\ \text{Ar}&\text{90%}&39.948&2.25&\text{87%}&88.98\\ \text{Total}&\text{100%}&71.9468&2.56&\text{100%}&101.325 \end{array} \right| $$
Argon is only ONE atom, it doesn't have any Ar<2>.
Values:
Concequesces:
$$ \left| \begin{array}{cc|ccc|c} \text{Gas}&\text{%}&\text{gr/mol}&\text{Mols}&\text{Fractal Mol}&\text{Partial Pressure (kPa)}\\ \text{O}_{2}&\text{10%}&31.9988&0.31&\text{13%}&13.44\\ \text{CO}_{2}&\text{90%}&44.01&2.04&\text{86%}&87.89\\ \text{Total}&\text{100%}&76.0088&2.35&\text{100%}&101.325 \end{array} \right| $$
There are several atoms, you can find the value in wikipedia or calculate by yourself (sum of all atoms * quantity values).
Values:
Concequesces:
You can see this interesting table that I found:
%CO2 in air Duration Major limitation
0.04 % lifetime normal atmosphere
0.5 % lifetime no detectable limitations
1.0 % lifetime "
1.5 % > 1 month mild respiratory stimulation
2.0 % > 1 month "
2.5 % > 1 month "
3.0 % > 1 month moderate respiratory stimulation
3.5 % > 1 week "
4.0 % > 1 week moderate respiratory stimulation, exaggerated respiratory response to exercise
4.5 % > 8 hours "
5.0 % > 4 hours prominent respiratory stimulus, exaggerated respiratory response to exercise
5.5 % > 1 hours "
6.0 % > 0.5 hours prominent respiratory stimulus, exaggerated respiratory response to exercise, beginnings of mental confusion
6.5 % > 0.25 hours "
7.0 % > 0.1 hours limitation by dyspnea and mental confusion
And this photo:
Well, 6 minutes at 7% CO2, think about at 90%...
$$ \left| \begin{array}{cc|ccc|c} \text{Gas}&\text{%}&\text{gr/mol}&\text{Mols}&\text{Fractal Mol}&\text{Partial Pressure (kPa)}\\ \text{O}_{2}&\text{10%}&31.9988&0.31&\text{1.37%}&1.38\\ \text{He}&\text{90%}&28.0134&22.48&\text{98.63%}&99.93\\ \text{Total}&\text{100%}&36.001402&22.79&\text{100%}&101.325 \end{array} \right| $$
Values:
Consequences:
$$ \left| \begin{array}{cc|ccc|c} \text{Gas}&\text{%}&\text{gr/mol}&\text{Mols}&\text{Fractal Mol}&\text{Partial Pressure (kPa)}\\ \text{O}_{2}&\text{10%}&31.9988&0.31&\text{31%}&31.72\\ \text{Xe}&\text{90%}&131.293&0.68&\text{68%}&69.59\\ \text{Total}&\text{100%}&163.29182&0.99&\text{100%}&101.325 \end{array} \right| $$
Values:
Concequences:
Well, sadly I can make calculations because I don't know the molecular mass of other elements but at least I can safestly say that obviously you would die of Hypoxia.
I hope this help you, sorry for the long post, I hate long post but you ask too much atmospheres. If you want more information check my others answers: this and this.
100% oxygen, nothing else - no the human body would go up like a gallon of gasoline with a static electricity spark, on top of it being toxic.
10% oxygen, 90% - carbon dioxide carbon dioxide of %7 can kill, long term exposure to %.5 can cause health issues.
for the rest humans to work OK need ~20 oxygen Less than 19.5% and you start feel severe effects and in General %10 is likely to lead to severe health issues including death.
10% is too little and wouldn't work. If you increased it to 20%:
100% oxygen:
20% oxygen, 80% nitrogen
20% oxygen, 80% argon
20% oxygen, 80% carbon dioxide
-Carbon dioxide is toxic at this level, we'd die.
20% oxygen, 80% helium
20% oxygen, 80% xenon
Edit in a caveat - I'm unsure how water (air humidity) changes in these environments. FOr example, water diffuses much quicker in Helium, which should mean humidity spreads out quicker and further making it harder for clouds to form.
You basically need oxygen to breathe. Everything else is not strictly necessary. The limits you are willing to take depend on how much of a mountaineer and how much of a diver you are.
These two articles explain the upper and lower limits for oxygen partial pressure for humans: https://en.wikipedia.org/wiki/High-altitude_adaptation_in_humans https://en.wikipedia.org/wiki/Maximum_operating_depth
Where the Tibetan highlanders live, the oxygen level is only about 60% of that at sea level. Most people will tolerate this level as a minimum, so you will have ~100mbar/10kpa of pure oxygen as a "minimum atmosphere". Breathing pure oxygen works well, as every tech diver will tell you. Still, everything that's not wet or otherwise inflammable will burn VERY easily. A little oil and a spark and you have a BIG fire.
Then you need to make sure that the amount of a lot of gases that are more or less poisonous are not too high. There's a partial pressure for each gas that you'll have to keep below a threshold.
Maximum partial pressures for some gases
Oxygen has been treated above, e.g. 1.6 bar - see https://en.wikipedia.org/wiki/Maximum_operating_depth
Nitrogen - e.g. 6 bar - see https://en.wikipedia.org/wiki/Nitrogen_narcosis
Hydrogen - e.g. 50 bar - see https://en.wikipedia.org/wiki/Hydrogen_narcosis
Argon and similar - e.g. 1 bar - see https://en.wikipedia.org/wiki/Argox
CO2 - e.g. 100 mbar - see https://en.wikipedia.org/wiki/Carbon_dioxide#Toxicity
Some effects may be additive. You could set up an atmosphere e.g. consisting of 1 part O2, 40 parts H2, 5 parts He and 5 parts N2 at a total pressure of fifty times the pressure on earth and you could breathe it, although you will feel the air being very "think" and you will need to get accustomed to it. You could also live in a 500 times thinner atmosphere made up of pure oxygen. That's about the limits for humans.
