Indoor plants have a great reputation for purifying the air in our homes. In Air Purifying Plants – Do They Work?, I debunked the idea that houseplants remove VOCs (toxic chemicals) from our home – it is just a well publicized myth. Several people commenting on that post and the post called A Garden Myth is Born – Plants Don’t Purify Air, to make the point that plants do more than remove chemicals – indoor plants increase oxygen levels in the air. This increased oxygen contributes a lot to our well being – or so people claim. Do houseplants increase oxygen levels in the home?
Plants and Photosynthesis
Through photosynthesis, plants combine CO2 with water and produce sugars and O2 (oxygen). Everyone accepts this fact. In nature, the production of oxygen is so important that without plants we would soon use it up and die.
Logically it follows that plants in a home would also contribute a significant amount of oxygen. There is no doubt that they produce oxygen, but how much do they produce? Is the amount significant compared to the amount we consume? Does a home with plants have a higher oxygen level than one without?
Good Quality Oxygen
A number of websites suggest that plants produce a good quality of oxygen. There is no such thing. Oxygen is oxygen. It is a simple molecule and the oxygen produced by plants is exactly the same as the one found in air.
How Much Oxygen Do Humans Consume?
The science of oxygen use by humans is well understood (ref 1). An adult uses about 550 L of oxygen per day.
How Much Oxygen Does a Plant Produce?
The amount of oxygen that a plant produces is much more difficult to calculate because it depends on many variables. Plants produce oxygen as a byproduct of making sugars, which is their energy source. Slow growing plants need much less sugar than fast growing plants, and therefore produce much less sugar and oxygen.
Low levels of light affect photosynthesis and result in less oxygen production. Temperature, water levels and available nutrients also impact photosynthesis and in turn oxygen levels.
Photosynthesis in a plant results in the plant getting carbon from the air and adding it to its body – leaves, stems and roots. Each molecule of CO2 absorbed, adds one atom of carbon to the weight of the plant and produces one molecule of O2. We can therefore get an estimate of the amount of oxygen produced by weighing the plant.
Marco Thorn has made this estimate and concluded that “for every 150 grams of plant tissue grown, 32 grams of oxygen are released. This is 22 liters of oxygen under normal temperature and pressure” (ref 2).
Plants Also Produce Carbon Dioxide (CO2)
Photosynthesis converts CO2 to O2, but plants also respire. During respiration they convert sugar and oxygen into CO2 and water. This is the reverse of photosynthesis, and it happens in all cells, all of the time, day and night.
Over time plants get bigger and heavier due to the carbon they accumulate. Therefore we know that the amount of CO2 produced from respiration is less than the CO2 used in photosynthesis – or else they could not grow.
Respiration reduces the net amount of oxygen plants produce, especially at night when there is no photosynthesis.
Plants vs Humans
Humans consume 550 L oxygen per day (ref 1). How much plant growth do we need to produce that amount of oxygen?
Plants produce 22 L for every 150 g of growth (ref 2). They would need to increase in weight by 3.75 Kg (8 pounds), each day, to produce the oxygen used by one person.
Keep in mind that plants grow slowly. Adding 3.75 Kg to your houseplants every day would require a huge number of plants.
In most homes the plants cannot produce oxygen at anywhere near the amounts we consume.
Do Indoor Plants Improve the Air?
So houseplants can’t supply all the oxygen we need, but do they increase the oxygen level?
From the NASA Fact Sheet we know that air contains 20.95% O2 and 0.04% CO2. If you had enough plants in a room to use up all of the CO2 and convert it to oxygen, the oxygen levels would increase from 20.95% to 21% (ref 3). This increase is difficult to detect and would have no effect on humans. Keep in mind that this increase is the maximum increase possible and assumes plants would use all the CO2 available. In real life the increase is even less.
Do Houseplants Increase Oxygen Levels?
Not really. They do add oxygen to the room, but in such small amounts that their contribution is negligible. People have a much larger effect on O2 and CO2 levels in a room than plants. If you want to live in a higher oxygen environment – get rid of the spouse and kids!
The main factor contributing to good oxygen levels is the ventilation rate – the exchange of air with the outdoors.
Grow houseplants because you enjoy them – not because they will improve the air in your home.
References:
- How Much Oxygen Do We Inhale; https://www.reference.com/science/much-oxygen-inhale-exhale-b763252ad5727e56
- Oxygen Produced By Houseplants; http://www.madsci.org/posts/archives/1999-02/917906305.Bt.r.html
- Do Houseplants Have an Impact on Oxygen Levels; http://skeptics.stackexchange.com/questions/6066/do-houseplants-have-any-impact-on-oxygen-levels
I have four Sansiverias in my bedroom and I feel the difference they made. Because of the smog and low temperature I don’t open windows in winter months. I sleep in a bed with my wife, so two persons lying next to each other produce CO2 for many hours. Plants are close to our heads, so you can say that we are the minority that have they noses right next to them, but I sleep and feel much better since I have them. The level of oxygen in the morning in my bedroom is significantly higher than it used to be and it is a fact you can feel, you don’t need a special equipment to measure it.
Your articles are very simplified. You give numbers about air that every kid learn, but you have forgotten that air is very different around the globe. In very polluted areas its % structure is different and this difference causes cancer in thousands of people every day. You write in English so many people around the world may read your articles and decide not to have plants, which may help them. You are so sure about being right and give opinions what most people do or what most people have (I assume you have travel a lot so you know what are the standards of living around the world) but don’t even notice that you put thousands of species (and milions years of evolution) into one word.
Re:”The level of oxygen in the morning in my bedroom is significantly higher than it used to be”. How did you measure these levels? What were the numbers? I’ll bet you did not measure them and that you really have no idea how they changed.
Re:”In very polluted areas its % structure is different” – do you have some reference to confirm this claim? Even if the values are different in a particular city, it does not change the fact that the amount of oxygen produced by plants will not change the values significantly enough to make a difference.
Thanks Robert! I just came with this idea of using home plants to improve the quality of air. Surprisingly it was not so easy to find any solid info on this topic, until I stumbled upon your article.
Can you provide sources for the claims I quote below? That would make the article even better:
“Humans consume 550 L oxygen per day. How much plant growth do we need to produce that amount of oxygen?
Plants produce 22 L for every 150 g of growth. They would need to increase in weight by 3.75 Kg (8 pounds), each day, to produce the oxygen used by one person.”
Thanks!
Konrad
The numbers come from the two references quoted. I have updated the post to include the reference numbers.
The composition of air you gave applies if it is fresh. If it is “stuffy”, the scenario of interest, it will be CO2 heavy and plants will have the potential to greatly improve its quality. This article ought to be corrected.
How does the CO2 level in fresh air compare to stuffy air? Without numbers your statement does not tell us much.
Robert, thank you for your detailed explanation.
So, plants don’t produce significant oxygen to make a difference & plants produce CO2 at night.
In my quest for better understanding this, hope you can shed some light on:
1. Looking at it other way would you say plants reduce significant carbon dioxide from a room?
2. How about Crassulacean acid metabolism in many of succulents?
No, not in a normal room with a normal amount of plants.
Listen to this podcast segment from The New Yorker Radio Hour. It’s about indoor vertical gardening. They discuss depleting the CO2 in the room enough that the plants were stunted. A fascinating segment overall.
http://www.wnyc.org/story/farm-grows-newark-rerun
They are not talking about a normal room.
My apologies, Robert. I wasn’t contradicting you. I thought it was interesting that you could have enough biomass to deplete the CO2 in a room.
Thankfully I just stumbled on this article. Very well done. Is there another way to bring more oxygen in a room without leaving the window open on a freezing cold winter night?
Not really. But do you have a low oxygen level problem? In most homes this is not really a problem.
This is not how gases work in localized, real world events. You are using data for an aggregate O2 and CO2 analysis. In the real world, the immediate area surrounding the plant’s stomata will be rich in O2, significantly so. Lean nto a large, dense, leafy indoor plant, and inhale.
There is no way, logically, that that breath will only contain 0.05% more O2.
I can agree with “the immediate area surrounding the plant’s stomata will be rich in O2”, but most people do not have their nose right next to their plant, so I don’t understand your point?
Re: “There is no way, logically, that that breath will only contain 0.05% more O2.” – that is not my data. If you have more correct data or see a mistake in how it was calculated, please present it.
One consideration that should be tested: The average atmospheric concentration of CO2 at sea level is about 400ppm, (0.04%) as you state. However, the level inside of a home, office or gym full of sweaty humans, can easily rise above 1000ppm thanks to our own respiration. At 2000ppm you’d have trouble getting a full breath while moving around. At 3000ppm you’d start breathing like a the anonymous creep on the other end of a prank phone call.
This is all to say that while outdoor plants can only hope to convert 400ppm of atmospheric CO2 into O2, indoor plants may have the opportunity to convert far more CO2 because of its greater concentration. The limiting factor is the plants’ growth rate, rather than the amount of CO2 in the air.
I wanted to echo what eacornelius wrote. We have begun to measure the air quality in our office, and the carbon dioxide climbs up really high each day, over 2000 ppm. The average quantity in the outside air is around 500 ppm, so the quantity of carbon is 4 times its normal outdoor rate. During weekends, the rate in the office falls to between 470 and 530 ppm.
At rates over 1000ppm, the air in the office is noticeably stuffy and people are drowsy. In this sort of case, having indoor plants may make a noticeable difference in the air quality when the ventilation is poor.
The only fact I see is that you have high CO2 levels. Have you added some plants and remeasured the values?
I love your dry humour Robert.
If we get rid of the spouse and the kids we will have some time to get some fresh air in the garden
What humour? 🙂
Thank you. I have been telling people this for a long time (I work in a garden centre), but this info will help me articulate my argument much more clearly.
Good advice. Get rid of the cat and dog while you’re at it.
Seriously, if you did increase the oxygen level, would there be any real benefit? Other than during aerobic exercise, perhaps?
That is an interesting medical question I almost tried to answer – but that is not not specialty.
notice that I only read this to see how gentle you could be with the idea – not because there was any possibility that it would be found to be valid or useful