Would this atmosphere require humans to wear gas masks but perhaps get acclimated over time?

Question

I got some great feedback on this atmosphere already, so I decided to lower the oxygen levels as a result of the feedback.

I am creating an atmosphere for a planet in a science fiction book I am writing and want to make sure that this atmosphere is sustainable for intelligent aliens while also being relatively breathable for humans but they have to resort to using gas masks at first before they acclimate over a long period of time. I also want the gas masks because I know xenon settling into valleys and depressions creates a death zone when there is no wind and want to include that in the book. I know there are a lot of noble gases comprising my atmosphere, is that too unrealistic? The reason I have this is because I want voice to be distorted in an unusual way via the helium and xenon combination. Here is the edited atmosphere in question.

• Atmospheric Pressure at sea level: 0.81 atm
• Atmospheric composition:
• 58.02% nitrogen
• 14.72% oxygen
• 12.79% argon
• 7.41% helium
• 6.18% xenon
• 0.88% other gases (carbon dioxide, water vapor, etc.)

Extra info: Size is similar to earth although has slightly less land mass, one moon orbits planet as well

Goal: I want to make it so that normal humans could acclimate with time but initially it is unsafe and use gas masks. (I fear I may have overdone it with reducing oxygen levels past the point of acclimation)

Thank you for great feedback last time!

Answer 1

You are about at the limits on lack of oxygen. Earth's sea-level atmosphere has about 0.2 bars of oxygen. Humans in Tibet and South America have adapted over generations to 4000-5000 metres, the lower end of which matches your atmosphere with about 0.12 bars of oxygen. Fit people can acclimatise in a few weeks to Everest southern base camp, which is at 5,364 metres, but unfit or unhealthy people usually cannot. A stable population contains many people who aren't fully fit and healthy, who are going to need supplemental oxygen in your atmosphere.

Also, your planet isn't heavy enough to hang onto helium: it will escape reasonably rapidly on geological timescales, so finding so much in a natural atmosphere is implausible.

Having that much xenon in the atmosphere is also unlikely. It's only formed in supernova explosions, not in ordinary stellar nucleosynthesis. If you want to keep it, you also ought to have large amounts of other heavy elements around, which may be hard on your biosphere. Xenon is also a powerful anesthetic. I doubt you have enough to put people to sleep, but it may well impair their judgement.

Answer 2

People could mostly acclimate

The Death Zone (the altitude at which you need oxygen tanks to survive) is about 8000m. This is where you only get 35% as much oxygen as you do at sea level.

That said hikers often use oxygen tanks at elevations greater than 3000m to sustain physical exertion where oxygen is about 69% normal.

Altitude sickness for a person in average shape not exerting themselves too hard, can happen in altitudes as low as 2500m. 74% normal oxygen.

Considering these limits, you planet has about 56.8% normal oxygen. This gives you an equivalent amount of oxygen as you find on Earth at an elevation of 4523m.

While this is survivable it is far from ideal. El Alto-La Paz is the highest altitude major city at on Earth at about 3,870m (62% oxygen) suggesting that normal people don't adapt very well to elevations in excess of this however, smaller towns like La Rinconada can be found at elevations up to 5100 (53% oxygen), but hypoxia is a common heath problem, even among long term residents of this town.

Since your O2 levels are less than 69% your assumption that supplement O2 would be needed for most people at first is correct, and since your O2 levels are also lower than than 62%, it is unlikely the people in normal health could adapt to live thier comfortably without long term health concerns, but because your O2 levels are higher than 53%, we can assume life without a mask is sustainable if it absolutely had to be.

https://www.mide.com/air-pressure-at-altitude-calculator

Answer 3

Wow, that's a low oxygen level!

OSHA (The USA's Occupational Safety and Health Administration) says that oxygen levels below 19.5% is low oxygen. In your proposed range of about 14%:

Concentrations of 12 to 16 percent oxygen cause tachypnea (increased breathing rates), tachycardia (accelerated heartbeat), and impaired attention, thinking, and coordination (e.g., Ex. 25-4), even in people who are resting.

Smarter Every Day has an interesting and terrifying video about hypoxia and air masks. We could expect these people to struggle with basic tasks and have severely impaired higher-level thinking ability. I would expect this situation to be unlivable over extended periods and for a normal society to not function.

This also isn't accounting for reduced atmospheric pressure, either! The lower pressure would reduce the effective equivalent concentration even lower to about 12%

More Realistic Oxygen Levels

I would go with OSHA's recommendation: 16-19%. That's enough that people can function, but not well. Even at 19%, this would require an acclimation time for people who just landed. It would be noticable but still allow people to perform higher cognitive tasks.

Factoring in the lower pressure, erring on the higher end of this percentage gives you an effective equivalent of about 16%, just in the border of this range.

Some Humans Have Adaptations

Genetic adaptations! Various groups of people have been living at high altitude (and therefore low oxygen) environments for a long time without complications. These groups would have a distinct advantage in a low-oxygen world! It would be certainly worth your time to investigate these adapted groups further.