Air purifiers work best in a closed room environment and this worries some who are concerned that there wouldn’t be enough oxygen coming in when all doors and windows are closed. Yet recent tests in a real apartment — with as many as seven people in a small room — show less than 1% change in oxygen levels in a closed room.
Fears of Low Oxygen
Fears of low oxygen levels are easy to find. Quora user Arghya Roy, says a closed room running air condition leads to low levels of oxygen.
Playing on this belief, companies rushed in with products that fill this supposed void. For example, the popular Three Dad’s purifier claims to solve the oxygen problem by using “submarine technology” to create oxygen.
The logic is simple: The room is closed, humans breathe in oxygen, so oxygen levels should decrease over time. Or should it not?
Smart Air tested this question by tracking oxygen levels with an iBrid MX6. We used the Smart Air office as an extreme testing site because the humble Smart Air office has seven people packed into just 34.5m² room.
On top of that, the office windows and doors are sealed with insulation tape to prevent polluted air from getting in (the office has no central air system too). We tracked oxygen levels throughout normal workdays, keeping the door shut except for when people left and came back from lunch at midday.
Even in these extreme conditions, oxygen levels showed almost no change. By the end of the day, oxygen levels had dropped by 0.3%. Simply put, humans don’t take in as much oxygen as we think we do. Based on oxygen alone, estimates are that an average person could survive in a completely sealed room for 12 full days!
The Change Is in Carbon Dioxide
While oxygen levels are pretty much constant over the day, what does change is the amount of carbon dioxide in the air. Tracked by the Air Visual Node, carbon dioxide levels went from 0.08% to 0.35% — more than tripling over the course of a day!
How Can Carbon Dioxide Triple when Oxygen Remains Unchanged?
If humans breathe in oxygen and breathe out carbon dioxide, how can one remain almost unchanged while the other skyrockets? The key is that regular air has a lot more oxygen than carbon dioxide. Oxygen constitutes about 20%, while carbon dioxide is only 0.038% of the air. Thus, carbon dioxide is capable of tripling from such a small number, while oxygen is mostly unchanged.
Carbon Dioxide Can be Harmful
Although we don’t have to worry about running out of oxygen, too much carbon dioxide can be harmful. At levels in the Smart Air office during the test (1,000-3,500PPM), people felt drowsy and may even perform worse on cognitive tests.
The Simplest Ways to Lower CO2 Levels:
#1 Open your windows from time to time
Yes, periodically opening the windows will let in polluted outdoor air, but our tests have found that purifiers, take the Cannon and Blasts for example, can cut PM2.5 levels by 50% in just 10 minutes after closing the windows.
#2 Leave the windows opened, just a tiny gap
If you have a strong purifier, open the windows by just a bit and leave it there. Our tests have found that purifiers can still be effective even when the window is left opened.
#3 Get a place with a central air system
Choose an office or apartment with a central air system that brings in outdoor air (hopefully purified ones too). If your apartment or office, like many of the ones in China, doesn’t have a central air system, you can get an air exchange system installed. But it is expensive.
In indoor spaces, oxygen levels are not of much concern even though CO2 can be. So the next time you come across a marketing hype about purifiers that claim to create oxygen, you know you don’t quite need that. Breathe safe (and smart) folks!
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.