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
If we provide a indoor greenwall for office place with coverage area in 2M², do it help and improve indoor air?
The benefit you see will probably be due to higher humidity levels. No real effect on O2
Oxygen levels are rarely a problem for humans — I think it would be more interesting to talk about carbon dioxide, which at even moderate levels impacts our health and mental capacity (see https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037). And there is evidence that having a lot of plants in a room can decrease CO2 levels, especially if the room has poor ventilation (for example, see the following study: https://pdfs.semanticscholar.org/1bd6/11a293f255864ecddc5aa7a7fb0da39d9767.pdf).
The effects are not as pronounced as you may like, but they are there. Ideally you would simply open a window, but in smoggy city areas or in the winter this might not be an option.
So, houseplants can in fact improve the air in our home, contrary to your statement.
The second study is interesting, but not representative of the average home. You really can’t extrapolate this to a home situation.
The study concludes “Indoor plants could not only decorate the indoor spaces,
release of pressure and tiredness, they could improve the
quality of indoor air condition and reduce the pollutants in the
air. ”
But this study did not look at pollutants at all – so that conclusion can’t be reached by this study.
The conclusion says nothing about a normal home, nor does it tray to extrapolate their findings to a normal home. So your statement “So, houseplants can in fact improve the air in our home” is not correct.
Just to add that plant growth doesn’t necessarily mean the plant is getting bigger. Plant growth also means the plant is, for example, producing new leaves to replace old dead ones. The plant stays the same overall size, but is still producing oxygen.
Great! So equal weight is not really equal weight!
It’s also the same as saying a human must loose weight because they take in O2 and produce CO2.
Thank you very much, Gilbert!
How to calculate rate of O2 production and consumption in particular environment.pls reply me
not sure what you are asking.
I am keeping money plant inside my room, feels refreshing.
haha ,, get rid of spouse and kids . your very funny blogger .
Dear Robert, are you familiar with the work of Dr. B.C. Wolverton? Best regards, Daniel Ament
Yes – I am fairly sure one of the references is his work.
I am having Money Plant & Snake Plant in my room.. Is is safe to keep them in bedroom?
Yes
Everything that Robert Pavlis has stated is very accurate. This is coming from someone with a B.S. in biology and chemistry, M.S. in molecular biology, and has performed academic research on plant metabolism, and an avid grower of indoor plants. Plant respiration is directly tied to their metabolisms and growth rates. Those things occur far more slowly for most indoor plants to have any measurable difference in a house with just 1 human in it. I fancy indoor avocado trees, and they get quite bulky, but I don’t kid myself in thinking that my avocado trees are doing anything significant against the pounds of dust mites in my house eating the ridiculous amounts of dead skin my 6 house members flake off each day (ignoring my 2 cats and Australian red hound). I love plants. They are better than white walls for your psyche. They matter. Life matters. They are not super-powered though. I read a article from an organization promoting the planting of 6-8 trees per person globally because that is the type of balancing required to cancel a person. For air purification don’t be penny-wise pound foolish and believe in falsehoods.
I chuckled at your comedic response at the end. If you want to increase oxygen levels, get rid of your spouse and kids. Ha ha ha.