• Written by Christine Rowe
  • Technology Business Reporter

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Houseplants look beautiful, but do they purify the air?

Most people just don’t realize How many pollutants They roam indoors, where they usually spend most of their time.

For example, many of the products we use to clean and refresh our homes, schools, and workplaces add invisible toxins to the air.

“Fresh is not a smell,” says Anne Hicks, a pediatric pulmonologist at the University of Alberta.

“If you can smell it, there’s a chemical in the air that’s seeping into your nose. All of that is air pollution, whether it smells good or bad,” she says.

“Indoor air pollution is huge, and it’s a relatively unknown frontier, because even my neighbor’s house has a different air pollution footprint than my house,” says Dr. Hicks.

Indoor air pollution is very complex, little regulated, and often beyond individual control. For example, road traffic produces nitrogen dioxide, while moisture and structural problems in buildings can lead to mold.

Air purifiers with high-efficiency particulate air (HEPA) filters can help. But the initial cost plus the energy required to operate it may be out of reach for some families.

This is one reason why it’s a good idea to think of potted plants as passive, inexpensive air cleaners. Essentially, plant leaves absorb carbon dioxide and other pollutants, which are then used in various plant processes or broken down.

Particularly important here is the presence of the microorganism community and the growing medium (such as soil or compost), which in many studies uptakes more contaminants than the plant itself.

An influential 1989 NASA study found that indoor plants can remove formaldehyde and other volatile organic compounds (VOCs) from the air. But the study was unrealistic to real-world conditions.

In essence, an indoor forest would be needed to measurably reduce VOCs in the home.

“You need a very large number of plants in a well-lit space to make any measurable impact on removing VOCs and many other gases,” says Tijana Planosa, principal horticulturist at the Royal Horticultural Society, and researcher at the Royal Horticultural Society. University of Reading.

Likewise, for carbon dioxide, “you need very large numbers of plants to have measurable room-level impacts.”

So is scaling up the solution?

Image source, Paul de Bois

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Green walls are expensive and need a lot of care

Some researchers, including Tijana Planosa, have moved from individual potted plants to active (living) green walls, which can concentrate more plants and also filter the air more efficiently due to the way air can be moved through them.

She explains that with active green walls: “Air is forced out of the room or stimulated through the root systems above the level which would happen naturally if the plants were potted.”

However, installing and maintaining these green walls is expensive.

So people keep experimenting with plants.

When construction consultancy Condal moved to its current London office in 2015, it filled one of the meeting rooms, known as the Green Lab, with plants.

The goal was to monitor and record the effect of plants on indoor air quality. But it was difficult to take care of them all.

It also became clear that plants did not have the same impact on air quality as mechanical ventilation and air filtration systems.

The room now contains a few larger plants in the corners, as well as a small rectangle of preserved reindeer moss on the wall. Spongy moss is nice to touch and look at, but it does not have the ability to absorb pollutants.

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Kavita Kumari says plants have a modest impact on air quality

When clients ask about plants to improve air quality, Kavita Kumari, associate director of Condall’s London office, advises them on the plants’ advantages and limitations.

She recommends plants that are relatively low-maintenance, while at the same time being able to reduce some VOCs and produce oxygen, although she admits these effects are modest.

One such plant is the snake plant (a popular houseplant that is also sometimes known as the sexist mother-in-law’s tongue, due to its sharp shape).

Ms Kumari says that while most plants absorb carbon dioxide and release oxygen during the day, this plant is able to do so at night as well.

Simply opening a window to allow indoor air pollutants to flow outside doesn’t work in highly built-up areas, where outside pollutants can enter at the same time, she says.

Scientists are working on a new generation of bioengineered plants to make them particularly effective at purifying the air.

Researchers at the University of Washington have genetically modified pothos plants using a synthetic version of the “green liver” protein found in rabbits, which can process chloroform and benzene.

Neoplants has also modified genes in pothos plants to enable them to essentially recycle some volatile organic compounds. In addition, the company has produced beneficial bacteria that are particularly effective at breaking down volatile organic compounds, which are delivered to plants’ root systems. It is this microbiome, not the plant itself, that produces most of the air-purifying effects of plants.

However, even improving NASA’s results by 30-fold, as Newplants claims, would not make it possible to rely on plants alone to clean the air.

Image source, Antoine Guillot/Newplant

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Modern plants have modified the genes in pothos plants

Ms. Kumari advises clients on adhering to the goals set by the WELL Building Standard, a certification for buildings that promote health and well-being. One of these goals is to cover 1% of the indoor space with plants.

This target falls into the category of “mind” rather than “air,” suggesting that the evidence for the benefits of indoor plants is stronger for mental health benefits than for air quality benefits. As Ms. Kumari comments, “Plants give you a sense of calm.”

Ultimately, air quality experts still favor indoor plants. But we shouldn’t expect the world of our potted friends.

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