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Normal levels of oxygen in atmosphere is around 21%. Recently in a discussion somebody commented that the polluted cities like Delhi has only 11% of oxygen in its atmosphere on some peak days of pollution. Can this be really true? Even if lot of pollutant gases like Carbon Monoxide are pumped onto atmosphere by vehicles and factories, can they replace so much oxygen?

Note : The full claim from the person was something specific like the day Barak Obama visited Delhi, the city's oxygen level was at 11%. Unfortunately neither he can give a citation for this nor I can find a news report about this claim. So I fear this question has to be closed due to the site guidelines.

PermanentGuest
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    11% would equate to a partial pressure of about 110 millibar. I'm pretty sure that's well below the minimum required to sustain human life. – GordonM Jun 07 '16 at 10:20
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    Even in a *really polluted city* you still have something like ~78% nitrogen, ~21% oxygen, ~0.9% argon and only ~0.1% of everything else. By the way: it was recently asked on a SE site what would happen if suddenly no new oxygen was introduced in the atmosphere by plants & algae. Result: nothing. Or better: the oxygen would last for thousands of years, which means we will all die of something other than oxygen depletion. So it's pretty absurd that a bit of pollution would halve the oxygen in the air. – Bakuriu Jun 07 '16 at 11:07
  • @Bakuriu: Do you have link for this question? – PermanentGuest Jun 07 '16 at 11:25
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    Skeptics is for unreferenced *notable* claims. "My friend said" is off-topic. – PointlessSpike Jun 07 '16 at 11:30
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    @PermanentGuest Found it here: http://biology.stackexchange.com/questions/46125/how-long-could-earths-oxygen-supply-last-if-no-new-oxygen-were-produced – Bakuriu Jun 07 '16 at 11:34
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    @Gordon True. Tech divers *do* use gas mixes with lower than 21% oxygen, because oxygen becomes toxic at a certain pressure, but anything below 18% oxygen cannot be used safely at the surface. (Consequently this also means that if the city was under high pressure, 11% oxygen levels could be safe.. apart from all the other hazards). – Voo Jun 07 '16 at 11:57
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    @GordonM: No, I don't think that would be the issue. That's the partial pressure of oxygen you'd find at an elevation of about 5500 meters above sea level, where the atmospheric pressure is about 500 millibar, according to [this graph from Wikipedia](https://en.wikipedia.org/wiki/Atmospheric_pressure#Altitude_variation). That's about the elevation of Russia's Mount Elbrus, or Everest Base Camp. Acclimatized people live just fine there. People have climbed Mount Everest without supplemental oxygen, where the oxygen partial pressure would be about 63 millibars. – Nate Eldredge Jun 07 '16 at 12:45
  • The biggest air issue in Delhi is excess particulates. The critical local oxygen issue is about water pollution and the lack of dissolved oxygen in the Yamuna river. – Henry Jun 07 '16 at 15:34
  • The only way oxygen reasonably could have disappeared from Delhi would be combustion (whether by biology or machine.) The output is at best one molecule of CO2 per oxygen molecule removed. Taking the O2 level to 11% would take the CO2 level to 9%--and while you can survive 11% O2 at sea level 9% CO2 is quite another matter. The other product of combustion would be CO and that's far worse than CO2. Thus the threat posed by the O2 is irrelevant. – Loren Pechtel Jun 08 '16 at 04:16

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No, this is not possible. The health effects of such a low oxygen level would have caused mass exhaustion, headaches, symptoms such as bluing of the lips, and probably collapse among weaker citizens (source1 source2) since no such health effects were observed this cannot have occurred.

Jack Aidley
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    FWIW, the OP only says that O2 levels fall this low "on some peak days of the year". For how long would a person have to be exposed to such low oxygen for these effects to become noticeable? (It may indeed still be less than a day such that they'd be noticeable in this case, but that's important/relevant information that should be included in your answer). – eggyal Jun 07 '16 at 14:04
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    @eggyal, effects manifest very quickly -- seconds to minutes. It is unsafe to attempt to rescue a person from an enclosed low-oxygen (not necessarily no-oxygen) space without using an oxygen supply. See [here](http://www.airproducts.com/~/media/files/pdf/company/safetygram-17.pdf), for example. – PellMel Jun 07 '16 at 15:10
  • OSHA safety limits are far from the actual danger point, your sources aren't really of much use. Here's a much better link: http://classroom.synonym.com/minimum-oxygen-concentration-human-breathing-15546.html – Loren Pechtel Jun 08 '16 at 04:13