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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.

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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 7 '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 7 '16 at 11:07
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    Skeptics is for unreferenced notable claims. "My friend said" is off-topic. – PointlessSpike Jun 7 '16 at 11:30
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    @PermanentGuest Found it here: biology.stackexchange.com/questions/46125/… – Bakuriu Jun 7 '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 7 '16 at 11:57
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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.

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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 7 '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, for example. – PellMel Jun 7 '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: classroom.synonym.com/… – Loren Pechtel Jun 8 '16 at 4:13

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