Can the oxygen levels in a polluted city be as low as 11%? 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.

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.