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My goal is not to decorate the interior, but simply to purify the air. I wonder if having plants is the cheapest option to purify the air.

My concerns are as follows:

  • My bedroom is rarely lit, and even when the lights are on, the lights have low lumen (e.g. less than 300 lumens).

    Due to this lighting constraint, my concern is that this may make the plants not produce O2 but mostly produce CO2.

    Is there any plant that produces O2 even in the absence of lighting?

  • Maintaining plants can cost some money; is this the cheapest way to purify the indoor air?

    My goal is to purify the indoor air from VOCs, ideally also increasing O2 levels while lowering CO2 if possible, all while adopting the cheapest solution.

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    There is no plant that produces O2 without light because the light is used to make the O2. Commented Feb 11, 2023 at 9:06
  • Does the bedroom have a window? Is the window covered up? Are there trees in front of it? How big is the window? What direction is the window facing? You might have some light. That doesn't mean you could grow just anything just anywhere in that room, with just any treatment, though. Commented Feb 15, 2023 at 7:25
  • I say this because I know someone who has plenty of light who thought she didn't have enough light to grow plants. If there's enough natural light to see very well, you can probably grow something (the same isn't necessarily true of artificial light). Golden pothos plants are a good low-light choice, usually. Commented Feb 15, 2023 at 7:32

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The air purifying meme is based on a study by Nasa in 1989 and has been enthusiastically promoted by anyone who likes or sells plants. Other studies have found that when you do not put the plants in a sealed chamber with continuous light the results are inconclusive at best.

Plants are not an effective way to filter the air. The cheapest way to get fresh air is to open the window.

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  • ...if by fresh you mean full of pollution and allergens and smoke from my neighbor's BBQ? Commented Feb 11, 2023 at 20:07
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The reason humans metabolism engages in chemical reactions that release CO2 is because such reactions release energy. Therefore, reversing these reactions and converting CO2 to carbohydrates and the like requires energy. Plants get this energy from light. I don't of any other source of energy that plants could use to absorb CO2.

Furthermore, the plant to animal ratio on Earth is quite large. Suppose you eat a carrot. Then as you metabolize it, you will release an amount CO2 sufficient for a plant to make a carrot, or carrot-equivalent. So a plant absorbing that CO2 would have to make a carrot-equivalent of plant matter. How many carrot-equivalents do you eat per day? How long does it take a plant to make a carrot-equivalent? If we say "10" for the first question, and "a month" for the second, then you would need 300 plants to absorb your CO2. And if multiple people are in the room at once, then you'll need even more Even if you aren't spending all of your day in the room, for the time that you are in the room, you're going to have to have the full CO2 absorbing capacity, unless your time in the room is short enough that CO2 doesn't build up.

There's also the fact that "stale air" is not just about CO2. There's all sorts of other issues, such as sweat.

Rooms aren't generally air-tight, and basic ventilation is generally enough to deal with CO2. If it's not, it's much easier to build a more advanced once than to fill the room with plants.

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  • Thanks for chiming in. Fascinating analysis about the quantity of plants required to undo the CO<sub>2</sub> of few humans. Totally unrelated: following this line of thought, do you also think that Earth is over populated by animals?
    – caveman
    Commented Feb 11, 2023 at 19:12
  • Good points. Although the idea of purifying, when it was floated. Was to absorb other gases, not CO2. Gases such as formaldehyde. I have not seen anything scientific on it. Commented Feb 11, 2023 at 19:44
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Given no useful light, and no desire for plants of themselves, a HRV (heat recovery ventilator) or ERV (energy recovery ventilator) would be a better use of energy for ventilation to provide the desired effects.

Given VOCs being mentioned, an HRV would be more suitable, as the humidity recovery aspect of an ERV makes them more subject to recycling other things between airstreams.

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Whatever effect there is, you will probably get better results putting plants where there is light. Then you can leave doors open to circulate air from one room to another. An open door might, all by itself, improve the air quality in the room.

There seems to be no free lunch. Ficus Benjamina is often seen in shopping malls and hotel lobbies. One of the reasons often touted for this is that they supposedly absorb the kind of chemical released by ordinary floor cleaning chemicals. However, according to Wikipedia the Benjamin fig is a significant source of allergens.

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