Do indoor plants purify the air? Science says no

Nov 10, 2019 10 comments

A study states that air improvement is an exaggeration and that it would take up to 1,000 plants per square metre for its effect to be felt.

Do indoor plants purify the air
Do indoor plants purify the air

That plants are an excellent decorative element is something no one doubts. However, many give these indoor gardens the power to regenerate the air. But does this ability have a real basis? 

According to a new study by researchers at the University of Drexel, in reality this is simply an exaggeration, as opening a window would be much more useful for cleaning the room than having one of these pot plants.
"This has been a common mistake for some time. Plants are great, but they don't really clean the air in a room fast enough to have an effect on air quality in a home or office." 
Explains Michael Waring, lead author of the article published in the Journal of Exposure Science and Environmental Epidemiology and professor of architectural and environmental engineering at the Drexel School of Engineering.

Waring and one of his doctoral students, Bryan Cummings, reviewed a dozen studies spanning 30 years of research. After their analysis, they observed that, in reality, rates of natural air exchange or indoor ventilation dilute concentrations of volatile organic compounds.

Where the myth comes from

In 1989, NASA conducted an experiment that attempted to prove that plants could be used to remove chemicals from the air at space stations. 

To do this, a plant was introduced into a sealed chamber in a laboratory, where it was actually verified that the air was being renewed. However, these environments have little to do with a home or office, and the data from these studies were not further interpreted.

The Waring and Cummings review takes the data from potted plant research volumes one step further than NASA and similar studies by using them to calculate a measure called a "clean air supply rate," or CADR. 

They were able to do this calculation for almost every study and what they found in every case was that the rate at which plants dissipated harmful elements in a chamber was much slower than the standard rate of air exchange in a building, demonstrating the overall effect of plants on indoor air quality is not significant.

"CADR is the standard metric used to scientifically study the impacts of indoor air purifiers, but many of the researchers who conducted these studies did not look at them from an environmental engineering perspective and did not understand how buildings' air exchange rates interact.

How many plants does it take to clean the air?

Many of these studies showed a reduction in the concentration of volatile organic compounds over time, so it is likely that people have taken advantage of them to exalt the air purification virtues of plants. 

But according to calculations by Waring and Cummings, it would take between 10 and 1,000 plants per square metre of space to compete with the air-cleaning capacity of a building's air management system or even just a couple of open windows in a house.

Nasa clean air study

"This is certainly an example of how scientific findings can be misleading or misinterpreted over time," Waring says. "But it's also a great example of how scientific research should continually re-examine and question the findings to get closer to the basic truth of understanding what's really happening around us.


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