# How Do I Supplement Oxygen Intake?

Series Premise Made Short: For reasons that I'm not allowed to describe here (confidentiality), Earth's deciduous and tropical plant life largely dies off. A hardy and oxygen-hungry microbe infests the dying soil and mankind starts to suffer from oxygen deprivation and CO₂ poisoning.

This is projected for year 2062, so tech has improved. What are simple theories for how people can survive on the surface without taking shelter in climate-controlled environments with fancy equipment? Basically, I'm looking for oxygen supplementation that the layman can get a hold of.

And, of course, the level of oxygen deprivation that they can reasonably handle and still survive indefinitely.

EDIT: Thank you guys for the detailed feedback. Because of the level of implausibility in the premise for the show, I've gotten permission to rework it, and even to share some of the details. I will obviously be registering with WGA to protect the premise of the show, but I'm making a new thread with more details and less BS. Thanks Again!

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• For the record, you could comfortably kill off all life on the rocky surface and be completely fine. It's the oceans that produce almost all of the breathable oxygen – Richard Dec 10 '16 at 19:54
• @Valorum in other words, we want a scientifically plausible solution to a scientifically implausible problem. – Broklynite Dec 10 '16 at 20:18
• @Broklynite - What I find interesting is that he's trying to rip off the first twenty minutes of Interstellar... :-) – Richard Dec 10 '16 at 20:53
• +1 for actually coming here trying to get this right rather than throwing bullshit into production. – R.. Dec 11 '16 at 3:41
• Again, thanks for coming here before writing! Others have jumped on the fact that oxygen mostly comes from the sea. But I’ll point out that if CO₂ built up to toxic levels, we’d have much worse to worry about. – JDługosz Dec 11 '16 at 11:38

First of all, the premise is a bit off. Something like 70% of the oxygen generation on Earth is done by plankton in the oceans, so a blight which kills land based plants will be somewhat inconvenient in terms of O2 production, the real problem in that case is people are going to get pretty hungry pretty fast with the destruction of the terrestrial food chain.

However, I'm going to pretend I didn't read the question fully and only got "blah, blah blah, O2 production is in rapid decline", which leads to this answer.

The issue of lack of oxygen really does not become a problem for life until the level drops considerably below the current level of 20%. Exceptionally conditioned people can actually climb to the top of Mount Everest without supplementary oxygen (although I certainly would not reccoment this for the vast majority of people), and large populations live at high altitudes in locations as varied as Bolivia or Nepal where the partial pressure is lower (the actual percentage of Oxygen is still @ 20%, it is just the air is so much thinner. By the time you get to the top of Everest, it is like having 33% less O2 per breath....). Translating this to your fictional scenario, this would suggest that we would not get into trouble until the percentage of oxygen in the atmosphere is reduced by 6% (from 20% to @ 14%). This is going to take some time given the massive amount of gases in the atmosphere, so people will not suddenly drop in the street gasping for air.

Even at lower partial pressure, you can still get along so long as you are supplementing the O2 intake. Carrying around bottled O2 is the current solution, but only works for limited amounts of time. To supplement your breathing Oxygen intake, I would suggest a zeolite filter with internal pores sized to permit the free flow of Oxygen molecules, but rejecting other, larger molecules like CO2 or Nitrogen.

Since pulling air through a filter requires energy, and a super fine filter sized to discriminate against molecular species will need considerably more energy to use than simply breathing hard against the filter. You will need a small electric motor to power a compressor to force air through the filter (or create enough suction to pull air through the zeolite) and from there into a facemask for you to breath through.

The canister which contains the device may be small enough to fit in a backpack (with solar cells covering the back, and a battery backup for nights and rainy weather), and will need an air intake, and exhaust port to eject the deoxygenated air and some sort of air hose to connect it to the facemask. How the production designer chooses to do this is up to him, but this should not actually be really large or heavy, and would mostly be in a backpack to ensure everything is protected, the weight is centered on the body and solar cells have relatively free exposure to the sun. A Fireman's air pack might be a suitable model, with the tank replaced by the apparatus.

Let us know when production starts.....

• Air pressure at the top of Mount Everest is 33.7 kPa, compared to 101 kPa at sea level. According to Wikipedia. – kingledion Dec 10 '16 at 21:49
• IDHL CO2 problem is not only lack of oxygen, but presence of CO2 too in first place. Equilibrium between binding with CO2 or O2 for hemoglobin kinda "barely enough to breath". And by removing CO2 as competitor you may have pretty low concentration of O2 still survivable (at least half, as people can live with one lung) so tiny compressor which removes CO2 just by liquefaction may be technologically less demanding solution and will work until certain concentration of Oxygen. And that is kinda Everest situation. – MolbOrg Dec 10 '16 at 22:01
• @Thucydides + MolbOrg: This is absolutely fantastic. Thanks. This is why I go to people smarter than before I propose concrete details. And sure thing, I'll let you know when production starts. – SirenKing Dec 10 '16 at 23:03
• Note that there are such portable oxygen supplies in fairly common use today, for people with heart & lung diseases, as well as pilots flying non-pressurized aircraft at higher altitudes. – jamesqf Dec 11 '16 at 19:17
• portable oxygen concentrator en.wikipedia.org/wiki/Portable_oxygen_concentrator – John Dec 11 '16 at 21:02

Humans can deal with fairly low levels of oxygen, but a raised level of CO2 is of concern. On space stations, fluctuations in the O2 level are routine, but fluctuations in the CO2 level would be an emergency situation, as that would indicate the failure of the CO2 scrubbing system.

Pre-industrial CO2 was about 280ppm and now it is about 400ppm (with significant local and seasonal variation). At over 1000ppm the raised CO2 level starts to interfere with gas exchange in our lungs, and we start to get tired easily. Over 2000ppm and you start to get ill. 5000ppm is the work place limit, although by then, sensitive individuals may already be drowsy and nauseous. 40000ppm (4%) is a level that would lead to brain damage and death. source

At these raised levels the Earth's greenhouse system is going to go haywire, there would be significant warming.

CO2 can be removed from air by bubbling it through an alkali solution, for example limewater (a solution of calcium hydroxide), unfortunately the production process for limewater requires large amounts of energy and produces even larger amounts of CO2.

Raised CO2 isn't nice, but in your scenario my first worry would be the collapse of the food cycle. Without crops people are going to get hungry real fast.

# How low does oxygen level have to be?

Altitude.org has a lot of information on oxygen levels in the blood stream at different altitudes. First, this page with charts shows the effects of 4000m altitude. 4000m is significant because this is about the highest that people regularly live at. There are very few permanent settlements above 4000m.

Oxygen partial pressure at sea level is about 21 kPa, corresponding with the 20% oxygen content in the air (since air pressure is about 101 kPa). At 4000m, oxygen partial pressure is 13 kPa, which means you only breather in about 60% as much oxygen in each breath at sea level.

This second page shows hemoglobin saturation plotted against oxygen partial pressure. At about 13 kPa partial pressure of oxygen saturation is still about 100%. At 8848m (the height of Everest), oxygen partial pressure is down to about 6.5 kPa. Looking at the hemoglobin saturation curve, hemoglobin saturation is down around 80 percent. I would consider a permanent year-round oxygen supply of 6.5 kPA to be fatal or close to it for most of the human population.

# How to explain your problem

The shape of the hemoglobin saturation curve suggests a solution. If oxygen levels get into the part of the curve around the 4–6 kPa range, then most people on earth would die. However, that means that you need very little added oxygen to induce a significant improvement in your health.

Let us say that oxygen partial pressure is 5kPa in your depleted earth. Since nitrogen partial pressure would stay constant at about 80 kPa, and nitrogen and oxygen are about the same sized molecules, the air is roughly 60,000 ppm oxygen. In order to get people to survive, lets say you want 10 kPa oxygen partial pressure; that corresponds to about 110,000 ppm oxygen.

Now here comes the math. A person's tidal volume (the amount of air taken in each breath) is about 0.5 liters, so to increase oxygen concentration of each breath from 5 kPa to 10 kPa, takes 0.5 × (0.11 - 0.06) = 25 mL of oxygen for each breath. You take 14 breaths per minute, so that is 0.35L per minute. Oxygen has a density of 1.49 g/L; so now you need 0.5 grams of oxygen to breath for a minute.

12 gram CO₂ cartridges cost about 50 cents a pop; pretty cheap. They are also small and lightweight. One of those, filled with oxygen, will be enough to breathe with for 24 minutes at the above calculation.

# Solution

A simple breathing mask, not gastight, but equipped with a valve designed to release a small amount of oxygen every time a breath is taken, with three 12 g cartridges plugged in would be lightweight (could be less than 1 lb), and provide enough oxygen for about an hour. A scuba tank has about 2180 liters of compressed air, and thus would provide about 100 hours of oxygen at the needed rate.

Because of the way the hemoglobin saturation curve is shaped, a small increase in oxygen can make a big difference between survival and death. If the world's oxygen levels are at one of the high slope parts of the curve, then a very modest oxygen supply can make a big difference.

# Unfortunately...

This still won't work. If you are writing popular sci-fi (or a TV show) hand-waving the inconvenient truths is probably just fine, but the fundamental problem is: where does the oxygen go? If you want to drop oxygen partial pressure from 21 kPa to 5kPa, you have to remove about $7.5\times10^{17}$ kg of oxygen. That is a lot.

There is essentially no conceivable metabolic process for your oxygen-eating microbes that does not turn oxygen into carbon dioxide. The only other possible molecule that is likely to soak up so much oxygen is water. Unfortunately, water needs hydrogen to make it, so to convert a a lot of oxygen to water, you need something with tons of hydrogen and no carbon (otherwise carbon dioxide will form).

There is one substance I can think of that is common, and fits the bill: ammonia. So great! These microbes react ammonia and oxygen to make water (and nitrous oxide) and make energy! Except that there just isn't that much ammonia on earth. If we were to add that much ammonia to earth, that would represent a comet made of solid ammonia about 50km across. Since the dino-killing asteroid was about 10km, adding 50 km of ammonia will cause many more problems than lack of oxygen, such as vaporizing the oceans.

So really, the only way to get rid of oxygen is to turn it into Carbon Dioxide. But if we turn rougly 3/4 of the Earth's oxygen into Carbon Dioxide, then now the atmosphere is 15% CO₂ (or 150,000 ppm). This is a problem because a. I can't think of any animals bigger than bacteria that won't die of carbon dioxide poisoning, and b. if you think global warming is bad at the current 400 ppm, wait until you see 150,000 ppm.

I can't think of a solution to your 'remove oxygen without extinguishing life on earth' problem, but if I do I will let you know.

• Well, yes and no. If these are largely oceanic microbes doing the work, then a significant amount of the CO2 might remain sequestered in the ocean instead of being released into the atmosphere. Of course, this would dramatically increase the acidity of the ocean and probably kill off vast swaths of life in the oceans, but it wouldn't necessarily result in a dramatic runaway greenhouse effect. – Salda007 Dec 11 '16 at 12:13
• @Salda007 The ocean cannot absorb ~ 1E18 tons of CO2. Much of that would outgas. – kingledion Dec 11 '16 at 13:18
• Surprisingly, it could absorb that much CO2, but, yes, it won't. The solubility of CO2 in water increases as temperature decreases and as pressure increases. But even assuming 1 atm of pressure, it's doable. Assume the water in the ocean is uniformly about 4º C. Solubility of CO2 at 4º C is ~3 g/kg. There's ~1.338e9 km^3 of water in the oceans, which can absorb 4.014e18 kg of CO2. 7.5e17 kg of O2 yields 1.03e18 kg of CO2, so you're only at 1/3rd capacity. The problem is, like you said, most of that would outgas until the pressures were at equilibrium. Biggest bottle of soda ever! – Salda007 Dec 11 '16 at 18:55

## Respirocytes and Oxygen Chambers

Respirocytes are hypothetical, microscopic, artificial red blood cells that are intended to emulate the function of their organic counterparts, so as to supplement or replace the function of much of the human body's normal respiratory system. Respirocytes were proposed by Robert A. Freitas Jr in his 1998 paper "A Mechanical Artificial Red Blood Cell: Exploratory Design in Medical Nanotechnology".

In Freitas' proposal, each respirocyte could store and transport 236 times more oxygen than a natural red blood cell, and could release it in a more controlled manner.

Such respirocytes would allow an adult human to sprint at top speed for at least 15 minutes without taking a breath.

## Oxygen Chambers (Refilling Environments)

So, with the respirocytes, people can survive in an oxygen depleted environment for much longer than they could otherwise. In order to refill their respirocytes, people could harness the oxygen-producing properties of algae to fill sleeping and working areas with plenty of oxygen. The algae could be given the excess CO2 and the resulting oxygen could be pumped throughout the facilities. Once people have their respirocytes filled, they can then go back out into oxygen deprived areas.

• I like the idea of people having an internal day-long supply of oxygen. But nanotech in the blood might not be the best approach, especially in a near future. – JDługosz Dec 11 '16 at 12:07

## Implement New Genetically Engineered Human Organs

In this idea, two new organs are developed via genetic engineering for human use. One is an oxygen producing organ, and the other is a carbon dioxide removing organ.

Depending on what feeling you want your show to have, you can either genetically engineer human DNA to produce these organs from birth, just like all other organs. This new strain of human DNA could be delivered to people via a retrovirus. This scenario could give the human society a feeling of extreme mastery of science, thereby setting a kind of "human greatness" theme for the show.

However, if you want a more desperate, dystopian feel for the show, you can simply have these organs grown or printed in labs and surgically inserted into humans at birth. This gives a less masterful feel to our grasp of science. Bonus: This scenario could also give rise to plenty of drama revolving around haves/have-nots (who can afford the surgery/organs), babies being born where organ implants are not easy or affordable, desperate "beat the clock" scenarios of getting the organs to surgery in time, etc. It also appeals to the "medical crisis" show demographic.

## The Oxygen Producing Organ

Human hair follicles already produce hydrogen peroxide naturally. So, genetically engineer an new organ from hair follicles that produces a large amount of hydrogen peroxide. This hydrogen peroxide can then be decomposed in this organ, releasing oxygen. The oxygen can then be integrated into the bloodstream.

## Blood Doping

Perhaps blood doping could be used by everyone so they always will have more oxygen in their blood stream, thereby making them less susceptible to oxygen deprivation during daily activities.

## The Carbon Dioxide Scrubbing Organ

Perhaps a human cell can be genetically engineered to produce carbon dioxide absorbing amines. This organ's structure should be such that the blood flows directly next to the amines so that the CO2 is absorbed through the blood vessel walls. Once the amines are saturated with CO2, they can be excreted via the normal eliminatory methods (urine or feces).

## Disclaimer

Do not try this at home unless several scientists are present. I'm not a geneticist, but I play one here on Worldbuilding. So, the hard science part of this may need some tweeking, but perhaps it can be better plausified by someone who knows more science stuff than I do. Good luck with your show!

• I don't think you can produce this hydrogen peroxide or any carbon dioxide absorbing stuff without actually using oxygen or producing carbon dioxide (in same or greater quantities). – Paŭlo Ebermann Dec 11 '16 at 14:11

In 1980, the great hard-SF writer Hal Clement tackeled this very subject in The Nitrogen Fix.

The story takes place well after the catastrophe and has people using certain devices and procedures to survive. Later they explain in more detail how these were developed as an emergency incentive to prevent extinction, as civilization was falling.

As I recall (it’s been a good many years), they had breathers based on biotechnology. The oxygen tanks are filled with tissue that can be grown even by the more primitive society that’s lost most technology. It acts like our red blood cells, grabbing oxygen from the air when the concentration is above a threshhold, and releasing it when the surrounding concentration is below a lower threshhold.

When “inside” they just have to hang up the tanks and they recharge themselves.

Now in more recent years I’ve seen reports of materials that absorb huge amounts of oxygen. Any sort would provide safe compact storage, but the two-threshhold thing makes it easy to just use, without regulators, a complex rebreathing apparatus, and concentrators for recharging.

Hal (actually Harry) also had a good explaination for the lack of oxygen which was revealed over the course of the novel. It didn’t break the hard-sf vibe or seem just plain stupid like so much TV, and was beleivable in the story. But it didn’t go into how much energy it would take, how much heqt would be released, and how much time it would take. The “metabolism” idea was kept vague enough to evade these questions, but still stays far away from things that knowledgable SF fans would “know” is nonsense.

I suggest they use solar-powered electrolysis to break apart the hydrogen and oxygen molecules in water to produce free oxygen. The hydrogen produced can then be used as fuel.

• One note about using the hydrogen as a fuel though. Burning it requires... oxygen. You can break apart water to get oxygen OR to store energy, but you can not have both at the same time. – Hohmannfan Dec 11 '16 at 17:00

## Where Did All the Oxygen Go?

Kinglidion brought up a point wondering how to get rid of all the oxygen without dangerously increasing the carbon dioxide in the atmosphere. So, here are some alternative oxygen-loss scenarios:

1. Divvying up Resources: Corporations begin off-world colonizing (either on planets, moons or space stations) and they must get their breathable oxygen from somewhere. Perhaps they are faced with a drastic problem: Earth is dying, so we must make a viable living space elsewhere, so people in all places (off-world colonies and on Earth) must share the oxygen, thus leaving one or more places oxygen deprived. Bonus: this could give rise to drama around who needs oxygen more, how to justify who gets it, will we run out if too many off-world colonies die and lose their oxygen, etc. Maybe also for some reason it's not cost effective or effecient enough to split water into oxygen and hydrogen.

2. Theft: People start to steal oxygen for their own colonies' use. Perhaps a wealthy colony decides to take as much oxygen from Earth as they can. Perhaps a group of hardened thugs takes more for their living space. There could even become a black market specializing in oxygen theft & smuggling. Bonus: Appeal to the crime show demographic.

3. Torn Away: A huge meteor passes right through Earth's atmosphere, missing the ground, but tearing away a huge chuck of our atmosphere, leaving us with just enough to survive. Perhaps many meteors from a meteor shower pass through once, or perhaps many meteors tear away atmosphere multiple times during the show. Bonus: drama around when the next devastating tear will be and how much more oxygen will be lost this time?

4. All of the Above: Oh boy are people in trouble now! Every worst case scenario has occured and now drama descends from all angles onto every demographic available!

• Dude, the question said that microbes ate the oxygen. – kingledion Dec 11 '16 at 2:20
• @kingledion Well, that's a good point. But, since you said in your answer that scenario gave rise to too much CO2, I tried to come up with alternative ways to get rid of the oxygen without uping the CO2. – Thom Blair III Dec 11 '16 at 2:24
• Oxygen is quite plentiful in the Solar System. On the Moon, it would be a waste product from extracting minerals from the regolith. Stealing O2 from Earth makes no sense at all. – Thucydides Dec 12 '16 at 16:53

How about genetically engineered humans who use anaerobic respiration instead of aerobic? They could sweat ethanol instead of sweating water from aerobic respiration. The ATP energy gained for the mitrochodira (cells battery) would be much lower though. I might therefore suggest photosynthesis alongside anaerobic respiration. They could be genetically modified with chloroplasts which live in their skin through a symbiotic relationship. The nice thing about the photosynthesis bit is that oxygen could be put back into the atmosphere!

## Bioreactor

Put a tank full of green algae out in the sun and bubble CO2-laden air through it, and let the algae convert it back into delicious, delicious O2 for you. You will need some method of preventing the microbe from infecting your tank, but that shouldn't be too tricky. You'll also need a power supply. A US Navy research paper from 1970 estimated that "approximately 2 ft^3 [of growing medium/culture] and 30 kW would be required to provide the oxygen needs of one man." Now, 30 kW is a lot of power, but that's using 1970s tech -- i.e. a big incandescent bulb. There's a 1994 paper here that investigates using LEDs to do the same thing. Their end result produced 10 mmol O2 per liter of culture per hour. Which more-or-less works out to about half of what the Feds got in 1970, but using a tiny fraction of the power.

The downside of a bioreactor is that you're basically looking at a tank of water surrounded by as many LEDs as you can pack in, along with a power supply, so it's not exactly the most portable technology. As I said, the 1994 team produced 10 mmol/hr per liter of culture. Unfortunately, people use more like 1350 mmol O2 per hour (sourcing from here and doing some unit conversion), so we're looking on the order of 135 liters (~35.6 gal) of growing medium, plus LED arrays and power supplies. That's fishtank-sized, and not a little desktop one.

I'm sure that we could improve the efficiency and production of the system with some system improvements and some selective breeding of algae, but you're always going to be looking at a bulky, water-filled system.

So that's your static home solution. For portable use, you want a

## Rebreather

Rebreathers for diving and for work in hazardous environments are already available commercially today. The technology is well over 100 years old at this point and very mature as a result. Modern backpack-sized units for diving allow several hours of operation, although they're more finicky than your standard open-circuit SCUBA set. However, given another 40-odd years of development and a very pressing motivating factor (like, say, atmospheric O2 being depleted to the point where it won't sustain life), I would guess that rebreather tech would be even more streamlined and reliable by the time period of your setting.

Alternately, there's

## Handwavium

Technology has advanced a lot in the past forty-six years. What's to say that ten years from now someone might invent a catalyst that allows for CO2->O2 conversion in a low-power, compact package? You'd need to find some way to get rid of the excess carbon, but on the whole it's certainly possible. Just as a starting point, there have been several recent developments in artificial photosynthesis, but those are focused more on solar-to-fuel production. If that tech is adapted to focus on CO2->O2 production, you could find yourself with a compact gas exchanger that is easy to manufacture and maintain. Which I suppose is basically a rebreather, but with product improvements such that you're not toting around a fickle canister of caustic chemicals.

Here is a crazy idea for conserving a few watts of oxygen/sugar metabolism: A nuclear powered artificial heart!

Think about the kind of nuclear power we sent to Mars aboard the Curiosity rover: The plutonium-238 fuel lasts a lifetime (half-time of 87.7 years) and its very pure alpha radiation can be shielded by just 2.5 mm lead, they say, so you shouldn't die of cancer too quickly.

There is only enough plutonium-238 in the world for a few select superhumans and spacecraft, so we wouldn't want to waste it on 5% efficient thermocouple technology as NASA is currently doing. A stirling engine equivalent has been made that is over 20% efficient. We just need to scale it down about 50 times, and use blood for cooling, but let's say we also maintain 20% efficiency. Say we aim for 3W at "the beginning of the mission", letting a battery take the peak load (since the rate of plutionium decay can't be controlled); that would require 15W of heat input to the engine, or 90g plutonium-238.

Even today, a nuclear heart should make you ideal for space exploration, and certain sports like freediving.