Earth Sciences and Ecology Question #9354

Anonymous, a 18 year old female from Montreal asks on November 7, 2016,

Is there a definitive answer as to whether it is harmful for your health to sleep with plants in the room, as they undergo cell respiration (and thus emit CO2) but not photosynthesis at night? My roommate and I have been arguing about this for weeks!

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The answer

Barry Shell answered on November 8, 2016

The answer is no. Plants in a bedroom are not harmful to your health due to their production of CO2 at night. This is an old wives tale. It’s really easy to work this out by simply looking at the normal amount of oxygen in air compared to CO2 in air. Air is about 21% oxygen. It is the second biggest component of Earth’s atmosphere. The rest is practically all nitrogen. After that there are only trace gasses, and CO2 is one of the trace gasses in the atmosphere. There is so little CO2 in air that it has to be measured in parts per million. And CO2 is one of the smallest trace gasses. There’s about 87 times more argon and water vapour in air than CO2. They are the biggest trace gasses. You can find this on Wikipedia under Atmosphere of Earth.  Even with us stupid humans burning up nearly half the oil, gas, and coal on Earth, thereby creating more CO2 than plants by far, still the amount of CO2 in air is only about 400 parts per million. To help you compare that to oxygen in air, divide 400 by 1,000,000, which is the same as 0.04% CO2 in air. Now compare that to 21% oxygen. There is 525 times as much oxygen in air as carbon dioxide. Even if the room was absolutely stuffed with plants, they would never be able to even get the concentration of CO2 up to 1% over one night, and this is assuming there are no doors, windows, cracks and that the room is hermetically sealed, which is very unlikely. If there is even a tiny crack, that super high concentration of CO2 would rush out of the room to reach equilibrium with normal air, which hardly has any CO2 in it at all. Even if the room was totally sealed in a tight plastic bag, you’d still have 20% oxygen to breath and you would not even notice anything. Actually in such an air-tight room, the biggest source of CO2 would be the humans. You and your roommate probably generate 100 times more CO2 than the plants. If you really want to reduce CO2 in your place at night, get rid of your roommate. LOL. 

Other thoughts: 
1. CO2 concentration needs to be 100 times normal before you even notice it when you breath. That is: around 4% CO2 you would start noticing it. You would feel like coughing, like when you accidentally inhale the CO2 that comes off a can of a carbonated beverage (pop or beer) when you first open it and pour it into a glass.
2. The plants in your room produce WAY MORE oxygen during the day than they consume at night, hence ON BALANCE they ADD more oxygen than they use. How do you think the earth got to have so much oxygen? It came from plants. Actually mostly from algae in the ocean, which is the main plant life on earth, since the Earth is basically mostly ocean. 
3. I have no idea why people want to go to live on Mars where the atmosphere is 95% CO2. Totally deadly. So if you are one of those people that worry about plants in your bedroom, make sure you don’t sign up for one of those trips to Mars.

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