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Houseplants don’t do much to improve indoor air, research review finds

According to the clean air delivery rate calculations, houseplants would reduce concentrations of volatile organic compounds over time in real-life indoor settings, but not very effectively.

Potted plants can make the rooms in your home or office more inviting and may even reduce your stress levels, but they’re not going to do much to improve the quality of the air in those indoor spaces, according to a new review of three decades of research on the topic.

Plants do clean indoor air, but not at a level that’s meaningful in most rooms, the review reports.

If you want cleaner air, you’d do better to open a door or window.

The idea that houseplants are useful indoor air filters “has been a common misconception for some time,” says Michael Waring, one of the study’s authors and an architectural and environmental engineer at Drexel University, in a released statement. “Plants are great, but they don’t actually clean indoor air quickly enough to have an effect on the air quality of your home or office environment.”

The study was published Wednesday in the Journal of Exposure Science and Environmental Epidemiology.

Three decades of data

As background information in the study notes, the myth of houseplants as air purifiers can be traced back to a 1989 project conducted by NASA scientists. While looking for ways to clean the air in space stations, they found that plants help remove volatile organic compounds (VOCs), such as formaldehyde and benzene.

But those NASA experiments — and subsequent ones done by other scientists — were conducted in small, sealed laboratory chambers into which a single VOC was introduced and its decay followed for hours or days. Such chambers are nothing like the rooms in which we live. Our indoor spaces have much larger volumes of air and steady streams of VOC emissions from multiple sources, including building materials, furniture, cleaners and other consumer products.c

They also have higher air-exchange rates due to the indoor air being constantly exchanged with outdoor air.

A different perspective

In the new review, Waring and one of his doctoral students, Bryan Cummings, decided to see what the laboratory findings from those earlier studies on indoor air quality and houseplants might mean for real-life settings. They selected and reviewed 12 of studies from the past 30 years. They then took the data from those studies and used it to calculate something called the clean air delivery rate, or CADR, which can take into account differences in air volume.

“The CADR is the standard metric used for scientific study of the impacts of air purifiers on indoor environments,” says Waring, “but many of the researchers conducting these studies were not looking at them from an environmental engineering perspective and did not understand how building air exchange rates interplay with the plants to affect indoor air quality.”

According to the CADR calculations, houseplants would reduce concentrations of VOCs over time in real-life indoor settings, but not very effectively.

The average rate of air cleaning observed in the 12 studies was 0.023 cubic meters per plant per hour. That compares to CADR of around 100 cubic meters per hour for a standard air purifier, Waring and Cummings point out.

It would therefore take between 10 to 1,000 plants per square meter (10.7 square feet) of floor space to clean a room’s air at the same level as an air purifier — or an open window, they add.

That number of plants would turn a room into a jungle-like greenhouse.

“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 reexamine and question findings to get closer to the ground truth of understanding what’s actually happening around us.”

FMI: You’ll find an abstract of the study on the website for the Journal of Exposure Science and Environmental Epidemiology, although the full paper is behind a paywall.

Comments (5)

  1. Submitted by Ray Schoch on 11/07/2019 - 08:32 am.

    I feel much less guilty now.

    I loathe humidity, which is why I still much prefer the climate of my former home in Colorado to my present one, and also why I haven’t opened a window in my Minneapolis house since I moved in a decade ago, except for a single instance to make sure the windows work as they should in case I need to escape in case of a fire. I’m generally a successful gardener outdoors, but my results with indoor plants could be characterized accurately as illustrations of plant-killing on an almost industrial scale. I’ve killed dozens, perhaps hundreds, of indoor plants over the years, including some that are generally regarded as indestructible, so I stopped buying indoor plants quite a while ago, and my home has no plants inside – at least none that I’m aware of.

    For years, I was vaguely aware of sentiments regarding improved air quality indoors due to plants, and it was a (small) part of why I kept buying indoor plants despite dismal results, but now I can put those sentiments back in the closet where, in my case at least, they apparently belong.

    • Submitted by Brian Simon on 11/08/2019 - 07:57 am.

      Ray, yes, plants are oversold as air purifiers, but note where they recommend you open a window! Fresh air is good!

  2. Submitted by Robert Moffitt on 11/07/2019 - 12:34 pm.

    I have always been suspicious of those claims.

  3. Submitted by Pat Terry on 11/07/2019 - 04:11 pm.

    Huh. Oh well, I still like my plants.

  4. Submitted by Be Joeshmoe on 11/09/2019 - 11:20 pm.

    Did they take into account the differences between plants? Philodendrons are supposed to be the most effective. Studying data of other studies hardly seems like a legitimate study in itself.

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